Answer
{$-5,-1$}
Work Step by Step
Using the rules for factoring trinomials, we obtain:
$3x^{2}+18x+15=0$
$3x^{2}+3x+15x+15=0$
$3x(x+1)+15(x+1)=0$
$(x+1)(3x+15)=0$
$(x+1)=0$ or $(3x+15)=0$
$x=-1$ or $x=-\frac{15}{3}=-5$
Therefore, the solution set is {$-5,-1$}.
