Expand these:

a. (x + 2)(x - 2)

b. (y - 4)(y + 2)

A. USE FOIL 
* first term squared, plus of minus, double the product, plus the last term squared 
^ A mathematical hymn which my math teacher taught me.

So:

a. x^2 - 2x +2x - 4
This can simplify to 
x^2 + 4 

b. y^2 + 2y - 4y - 8
This can simplify to 
y^2 - 2y - 8

 

Answer is a not really sure tho