index.js

//Soal No. 1 (Callback Baca Buku)
//===============================
console.log("//Soal No. 1 (Callback Baca Buku)");
console.log("//===============================");
// di index.js
var readBooks = require('./callback.js')

var books = [
    {name: 'LOTR', timeSpent: 3000},
    {name: 'Fidas', timeSpent: 2000},
    {name: 'Kalkulus', timeSpent: 4000}
]

// Tulis code untuk memanggil function readBooks di sini
var time=10000
var i=0;
function letsread(time,books){
    if(time>0 && i<books.length)
    readBooks(time,books[i],function(sisaWaktu){
        time=sisaWaktu;
        i++;
        letsread(time,books)
    })
}

letsread(time,books)