From the given problem :
x^2 + 11x + 28 can be factored as, you need to think of two numbers that has a product of 28 and a sum of 11. In this case it's 7 and 4 :
(x + 7)(x + 4)
and x^2 + 2x - 8 can be factored as, you need to think of two numbers that has a product of -8 and a sum of 2. In this case it's 4 and -2 :
(x + 4)(x - 2)
So the expression will be :
The term (x+4) will be cancelled out
Simplify further and the answer is :