Answer
{$-7,4$}
Work Step by Step
Using the rules of factoring trinomials, we obtain:
$n^{2}+3n-28=0$
$n^{2}-4n+7n-28=0$
$n(n-4)+7(n-4)=0$
$(n-4)(n+7)=0$
$(n-4)=0$ and $(n+7)=0$
$n=4$ and $n=-7$
Therefore, the solution set is {$-7,4$}.