If you meant (x^2 + 5x - 36)/(x^2-16) then the answer is: (x+9)/(x-4)
This is just factoring, you can use guess and check.
If you take just the numerator: x^2+5x-36 and factor. To factor consider -36, and the multiples that can add up to 5 (from 5x).
x^2 + 5x - 36/(x^2-16)
The denominator is actually a rule of (a+b)(a-b) which in this case (x+4)(x-4)
Now just divide like terms which is the (x-4)/(x-4)=1