diff --git a/lesson3/challenges/convertBlocking.js b/lesson3/challenges/convertBlocking.js
index d5364cc..deef690 100644
--- a/lesson3/challenges/convertBlocking.js
+++ b/lesson3/challenges/convertBlocking.js
@@ -3,5 +3,9 @@
 
 var fs = require('fs');
 
-var contents = fs.readFileSync('hello.html');
-console.log(contents.toString());
\ No newline at end of file
+// var contents = fs.readFileSync('hello.html');
+// console.log(contents.toString());
+
+fs.readFile('hello.html','utf-8', (err, data) => {
+  console.log(data);
+});
diff --git a/lesson3/challenges/copyFile.js b/lesson3/challenges/copyFile.js
index 72504a7..2c9e63b 100644
--- a/lesson3/challenges/copyFile.js
+++ b/lesson3/challenges/copyFile.js
@@ -1,6 +1,21 @@
 // Copy contents from hello.html to hello-copy.html
 var fs = require('fs')
 
+
 // 1. Do this synchronously first
+// const encoding = 'utf8';
+// const contents = fs.readFileSync('hello.html', encoding);
+// fs.writeFile('hello-copy.html', contents, encoding, (err) => {
+//   console.log(err);
+// })
 
-// 2. Do the same thing asynchronously
\ No newline at end of file
+// 2. Do the same thing asynchronously
+fs.readFile('hello.html', (err, data) => {
+  if (err) {
+    console.log(err);
+  } else {
+    fs.writeFile('hello-copy.html', data, (err) => {
+      console.log(err);
+    })
+  }
+})
diff --git a/lesson3/challenges/rectangle.js b/lesson3/challenges/rectangle.js
index 7486b12..2365eb1 100644
--- a/lesson3/challenges/rectangle.js
+++ b/lesson3/challenges/rectangle.js
@@ -33,9 +33,16 @@ function rectangle(length, width, callback) {
 
 function sloveRectangle(err, result) {
   // To be implemented
+  if (err) {
+    console.log(err.message);
+  } else {
+    // console.log(`- length: ${length}, width: ${width}`)
+    console.log(`- The area : ${result.area()}`);
+    console.log(`- The perimeter : ${result.perimeter()}`);
+  }
 }
 
 // Test
 rectangle(2, 4, sloveRectangle);
 rectangle(3, 5, sloveRectangle);
-rectangle(-3, 5, sloveRectangle);
\ No newline at end of file
+rectangle(-3, 5, sloveRectangle);
diff --git a/lesson3/challenges/tasks.js b/lesson3/challenges/tasks.js
new file mode 100644
index 0000000..1512f23
--- /dev/null
+++ b/lesson3/challenges/tasks.js
@@ -0,0 +1,75 @@
+/*
+$ node tasks.js list
+$ node tasks.js clear
+$ node tasks.js add <task>
+*/
+
+const fs = require('fs');
+
+const targetFile = 'tasks.txt';
+const defaultContents = '[]';
+let tasks;
+
+try {
+  tasks = parseFile(targetFile);
+} catch (e) {
+  fs.writeFileSync(targetFile, defaultContents, 'utf8', (err) => {
+    console.log(err);
+  })
+  tasks = parseFile(targetFile);
+}
+
+let command = process.argv[2];
+
+switch (command) {
+  case 'list':
+    listTasks();
+    break;
+  case 'clear':
+    clearTasks();
+    break;
+  case 'add':
+    addTask();
+    break;
+  default:
+    help();
+}
+
+function parseFile(fileName){
+  return JSON.parse(fs.readFileSync(fileName, 'utf-8'));
+}
+
+function listTasks() {
+  if (tasks.length === 0) {
+    console.log('Found no tasks.');
+  } else {
+    console.log('Found', tasks.length, 'tasks.');
+    for (let i = 0; i < tasks.length; i++) {
+      console.log(i + 1, tasks[i]);
+    }
+  }
+}
+
+function clearTasks() {
+  fs.writeFile(targetFile, defaultContents ,(err) => {
+    console.log(err);
+  });
+  console.log(`Cleared up the tasks. (${tasks.length} tasks)`);
+}
+
+function addTask() {
+  let task = process.argv.splice(3).join(' ');
+  tasks.push(task);
+  fs.writeFile(targetFile, JSON.stringify(tasks), (err) => {
+    console.log(err);
+  })
+  console.log(`Added the given task. (${tasks.length} tasks)`);
+}
+
+function help() {
+  console.log('-------------------- HOW TO USE --------------------');
+  console.log('$ node tasks.js list: list up all the tasks.');
+  console.log('$ node tasks.js clear: clear up all the tasks.');
+  console.log('$ node tasks.js add <task>: add the given task. ');
+  console.log('----------------------------------------------------');
+}
diff --git a/lesson3/challenges/tasks.txt b/lesson3/challenges/tasks.txt
new file mode 100644
index 0000000..0637a08
--- /dev/null
+++ b/lesson3/challenges/tasks.txt
@@ -0,0 +1 @@
+[]
\ No newline at end of file