diff --git a/Week4/homework/ex1-aggregation/index.js b/Week4/homework/ex1-aggregation/index.js
new file mode 100644
index 000000000..a11eaae7f
--- /dev/null
+++ b/Week4/homework/ex1-aggregation/index.js
@@ -0,0 +1,71 @@
+const { MongoClient } = require("mongodb");
+const url = "mongodb://localhost:27017";
+const dbName = "databaseweek4";
+
+async function getTotalPopulation(client, country) {
+  const res = await client
+    .db(dbName)
+    .collection("population")
+    .aggregate([
+      { $match: { Country: country } },
+      {
+        $group: {
+          _id: "$Year",
+          countPopulation: { $sum: { $add: ["$M", "$F"] } },
+        },
+      },
+    ]);
+
+  return res.toArray();
+}
+async function getInformationOfPopulation(client, year, age) {
+  const res = await client
+    .db(dbName)
+    .collection("population")
+    .aggregate([
+      {
+        $match: {
+          Year: year,
+          Age: age,
+          Country: {
+            $in: [
+              "AFRICA",
+              "ASIA",
+              "EUROPE",
+              "OCEANIA",
+              "NORTH AMERICA",
+              "SOUTH AMERICA",
+            ],
+          },
+        },
+      },
+      {
+        $addFields: {
+          TotalPopulation: { $add: ["$M", "$F"] },
+        },
+      },
+    ]);
+
+  return res.toArray();
+}
+
+async function main() {
+  const client = new MongoClient(url);
+  try {
+    await client.connect();
+    console.log("Connected successfully to server");
+    const totalPopulation = await getTotalPopulation(client, "Netherlands");
+    console.log("Total Population:", totalPopulation);
+    const informationOfPopulation = await getInformationOfPopulation(
+      client,
+      2020,
+      "100+"
+    );
+    console.log("Information Of Population:", informationOfPopulation);
+  } catch (err) {
+    console.log(err.message);
+  } finally {
+    await client.close();
+  }
+}
+main();
diff --git a/Week4/homework/ex1-aggregation/package-lock.json b/Week4/homework/ex1-aggregation/package-lock.json
new file mode 100644
index 000000000..5d3fe9f51
--- /dev/null
+++ b/Week4/homework/ex1-aggregation/package-lock.json
@@ -0,0 +1,645 @@
+{
+  "name": "ex1-aggregation",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "ex1-aggregation",
+      "version": "1.0.0",
+      "license": "ISC",
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+        "mongodb": "^6.19.0"
+      }
+    },
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+}
diff --git a/Week4/homework/ex1-aggregation/package.json b/Week4/homework/ex1-aggregation/package.json
new file mode 100644
index 000000000..64a0a2447
--- /dev/null
+++ b/Week4/homework/ex1-aggregation/package.json
@@ -0,0 +1,16 @@
+{
+  "name": "ex1-aggregation",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "mongoclient": "^1.0.3",
+    "mongodb": "^6.19.0"
+  }
+}
diff --git a/Week4/homework/ex2-transaction/index.js b/Week4/homework/ex2-transaction/index.js
new file mode 100644
index 000000000..4395031a8
--- /dev/null
+++ b/Week4/homework/ex2-transaction/index.js
@@ -0,0 +1,75 @@
+const { MongoClient } = require("mongodb");
+const url = "mongodb://localhost:27017";
+const dbName = "financeDB";
+async function insertAccount(client) {
+  await client.db(dbName).collection("accounts").deleteMany({});
+  const res = await client
+    .db(dbName)
+    .collection("accounts")
+    .insertMany([
+      {
+        account_number: 1,
+        balance: 5000,
+        account_changes: [
+          {
+            change_number: 1,
+            change_amount: 500,
+            change_date: new Date("2025-09-17"),
+            remark: "gift",
+          },
+          {
+            change_number: 2,
+            change_amount: -200,
+            change_date: new Date("2025-09-18"),
+            remark: "withdrawal",
+          },
+          {
+            change_number: 3,
+            change_amount: 300,
+            change_date: new Date("2025-09-19"),
+            remark: "deposit",
+          },
+        ],
+      },
+      {
+        account_number: 2,
+        balance: 3000,
+        account_changes: [
+          {
+            change_number: 1,
+            change_amount: 1000,
+            change_date: new Date("2025-09-17"),
+            remark: "salary",
+          },
+          {
+            change_number: 2,
+            change_amount: -500,
+            change_date: new Date("2025-09-18"),
+            remark: "bills",
+          },
+          {
+            change_number: 3,
+            change_amount: 200,
+            change_date: new Date("2025-09-19"),
+            remark: "freelance",
+          },
+        ],
+      },
+    ]);
+}
+
+async function main() {
+  const client = new MongoClient(url);
+  try {
+    await client.connect();
+    console.log("Connected successfully to server");
+
+    await insertAccount(client);
+    console.log("Inserted accounts");
+  } catch (err) {
+    console.log(err.message);
+  } finally {
+    await client.close();
+  }
+}
+module.exports = main;
diff --git a/Week4/homework/ex2-transaction/package-lock.json b/Week4/homework/ex2-transaction/package-lock.json
new file mode 100644
index 000000000..827af27e0
--- /dev/null
+++ b/Week4/homework/ex2-transaction/package-lock.json
@@ -0,0 +1,151 @@
+{
+  "name": "ex2-transaction",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "ex2-transaction",
+      "version": "1.0.0",
+      "license": "ISC",
+      "dependencies": {
+        "mongodb": "^6.19.0"
+      }
+    },
+    "node_modules/@mongodb-js/saslprep": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npmjs.org/@mongodb-js/saslprep/-/saslprep-1.3.0.tgz",
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+      "dependencies": {
+        "sparse-bitfield": "^3.0.3"
+      }
+    },
+    "node_modules/@types/webidl-conversions": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/@types/webidl-conversions/-/webidl-conversions-7.0.3.tgz",
+      "integrity": "sha512-CiJJvcRtIgzadHCYXw7dqEnMNRjhGZlYK05Mj9OyktqV8uVT8fD2BFOB7S1uwBE3Kj2Z+4UyPmFw/Ixgw/LAlA=="
+    },
+    "node_modules/@types/whatwg-url": {
+      "version": "11.0.5",
+      "resolved": "https://registry.npmjs.org/@types/whatwg-url/-/whatwg-url-11.0.5.tgz",
+      "integrity": "sha512-coYR071JRaHa+xoEvvYqvnIHaVqaYrLPbsufM9BF63HkwI5Lgmy2QR8Q5K/lYDYo5AK82wOvSOS0UsLTpTG7uQ==",
+      "dependencies": {
+        "@types/webidl-conversions": "*"
+      }
+    },
+    "node_modules/bson": {
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diff --git a/Week4/homework/ex2-transaction/package.json b/Week4/homework/ex2-transaction/package.json
new file mode 100644
index 000000000..2cac44d2d
--- /dev/null
+++ b/Week4/homework/ex2-transaction/package.json
@@ -0,0 +1,15 @@
+{
+  "name": "ex2-transaction",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "mongodb": "^6.19.0"
+  }
+}
diff --git a/Week4/homework/ex2-transaction/transfer.js b/Week4/homework/ex2-transaction/transfer.js
new file mode 100644
index 000000000..b59364f5a
--- /dev/null
+++ b/Week4/homework/ex2-transaction/transfer.js
@@ -0,0 +1,76 @@
+const { MongoClient } = require("mongodb");
+const url = "mongodb://localhost:27017";
+const dbName = "financeDB";
+const client = new MongoClient(url);
+
+async function transferAmount(client, fromAccount, toAccount, amount, remark) {
+  const session = client.startSession();
+  const transactionOptions = {
+    readPreference: { mode: "primary" },
+    readConcern: { level: "local" },
+    writeConcern: { w: "majority" },
+  };
+
+  try {
+    await session.withTransaction(async () => {
+      const db = client.db(dbName);
+      const accounts = db.collection("accounts");
+
+      const fromAcc = await accounts.findOne(
+        { account_number: fromAccount },
+        { session }
+      );
+      const toAcc = await accounts.findOne(
+        { account_number: toAccount },
+        { session }
+      );
+
+      if (!fromAcc || !toAcc) {
+        throw new Error("Account not found");
+      }
+      if (fromAcc.balance < amount) {
+        throw new Error(`Insufficient funds in account ${fromAccount}`);
+      }
+
+      await accounts.updateOne(
+        { account_number: fromAccount },
+        {
+          $inc: { balance: -amount },
+          $push: {
+            account_changes: {
+              change_number: fromAcc.account_changes.length + 1,
+              change_amount: -amount,
+              change_date: new Date(),
+              remark,
+            },
+          },
+        },
+        { session }
+      );
+
+      await accounts.updateOne(
+        { account_number: toAccount },
+        {
+          $inc: { balance: amount },
+          $push: {
+            account_changes: {
+              change_number: toAcc.account_changes.length + 1,
+              change_amount: amount,
+              change_date: new Date(),
+              remark,
+            },
+          },
+        },
+        { session }
+      );
+    }, transactionOptions);
+
+    console.log("Transaction committed");
+  } catch (err) {
+    console.error("Transaction aborted", err.message);
+    await session.abortTransaction();
+  } finally {
+    await session.endSession();
+  }
+}
+await transferAmount(client, 1, 2, 1000, "Rent payment");