I am trying to get better at math, the highest math I have is Algebra. For some reason I just can't do math. I have this homework helpers book about basic math and pre-algebra to help me understand math.

Its talking about negative integers and distributive property. I was following along just fine until I got to this example it asked me to work out.

25x96

Now I thought I had this, so I went about to do this:

(25x90) + (25x6) to get my answer but then I read how the book does it and I am completely lost. This is how the book did it:

25x96 = 25 x (100-4) = 25x100 + 25 x (-4)

= 2,500 - 100 = 2,400

Where did they get this 100-4, I realize it equals 96 but what? Can anyone explain to me why it went by 100? What am I missing here?