How is 4.09 grams obtained in this chemistry problem?

[Complexity]

Homework Statement

http://img842.imageshack.us/i/cusersbenappdatalocalte.png/

Homework Equations

The Attempt at a Solution

The work is inside the link. I am just wondering how 4.09 grams is obtained? Like how did the person know to take out 4.09 grams?

 

[epenguin]

Very likely in parts a or b which we can't see.

 

[Borek]

If you are too lazy to copy questions, I am too lazy to think about the answer.