Candice, if I am reading correctly, we can factor a out of the numerator.
a(a + 4)
We can also factor the denominator. We multiply a x c, 1 x -4 = -4. We need two factors of -4 that add up to equal b, 3.
-4 x 1 = -4, but - 4 + 1 = -3. Nope.
4 x -1 = -4 and 4 + (-1) = 3
a2 + 3x - 4 = (a + 4)(a - 1)
Sooooo, we have...
a(a + 4)/(a + 4)(a - 1)
What cancels out? a + 4/a + 4 = 1, soooo...
a/(a - 1) is our answer.
Hope this helps!