Answer
{$-1,4$}
Work Step by Step
Factoring the equation and setting the factors equal to zero, we obtain:
$3x^{2}-9x-12=0$
$3x^{2}+3x-12x-12=0$
$3x(x+1)-12(x+1)=0$
$(x+1)(3x-12)=0$
$(x+1)=0$ or $(3x-12)=0$
$x=-1$ or $x=\frac{12}{3}$
$x=-1$ or $x=4$
Therefore, the solution set is {$-1,4$}.
