Take the numerator of the fraction and factor it out.

Your fraction should now look like this:

Because (x+4) is present in both the numerator and denominator, you can cross it out. You should be left with
only (x-1) in the numerator.
x cannot equal -4, as if it is inputted in the denominator, -4 + 4 would equal 0. Dividing by 0 is impossible.