I assume you have 2 expressions here
1st one - X^2 + 2x – 15/x^2 + x – 12
x^2
2nd one - x^2 – 4x – 45/ x^2 – 5x - 36

The factors are -
(x-3)(x+5)        &nb... (x-9)(x+5)    
=======    and   =======   
(x-3)(x+4)        &nb... (x-9)(x+4)

Removing the common factors we get the answer for each expression to be the same i.e. (x+5)/(x+4)

If these expressions were being multiplies the answer would be (x+5)^2/(x+4)^2