I'm just reading through my algebra textbook and one of the example questions is solve the following

(2x+3)(2x+5)-4(x+9)(x-5)

where the answer is supposed to be an integer. I don't see how it can be an integer though because the xs don't seem to cancel out. Maybe I've done something wrong but this is what I've got so far:

2x^{2}+4x+21-4(x^{2}+4x-45)