Answer: x-2 (x not equal to -2 or -3)
Explanation:
Lets look at the bottom: x^2+5x+6= (x+2)(x+3)
Lets see if we can take out (x+2) or (x+3) from the top.
x^3+3x^2-4x-12= (x+2)(x^2+x-6) = (x+2)(x+3)(x-2)
So we get x-2 as solution.
The only thing you have to take care is not to divide by 0.
Thus x is not equal to -2 or -3.