Let's factor the first parenthesis.
X^2 + 4x -12
For this, we need to find what multiplies to -12, but adds to 4. (This skill gets faster and easier through time, but I will just tell you know the numbers are 6 and -2)
So it becomes:
(X+6)(x-2)(x-3)
So your roots are:
6, -2, and 3.
I hope this Helps!