"This" exercise


I don't see how my code is wrong here? Help appreciated.

// here we define our method using "this", before we even introduce bob
var setAge = function (newAge) {
this.age = newAge;
// now we make bob
var bob = new Object();
bob.age = 30;
bob.setAge = setAge;

// make susan here, and first give her an age of 25
var susan = new Object();
susan.age = 25;

// here, update Susan's age to 35 using the method


You didnt use your method setAge on your Object susan

Do this

susan.setAge = setAge;


I am stuck on this lesson too. What exactly does this line of code do?
susan.setAge = setAge;