SOLUTION: 12a²-4a-16. I got this far 4(3a²-a-4) and I know that the answer is 4(3a-4)(a+1) but not sure how to get to that conclusion. Thank You

[To get ² hold down Alt while typing 253 on the keypad at the far right
of your keyboard with NumLock turned on.  To get ³ do the same but
type 0179 on the keypad.  Don't use the number keys above the letter keys.
They won't work.]

4(3a²-a-4)

You need to learn how to factor 

3a²-1a-4.

Here is a tutorial I wrote on how to do that. Go here

http://www.algebra.com/my/change_this_name32371.lesson?content_action=show_dev

Edwin