Answer
$(s-6t)(s+2t)$
Work Step by Step
The 2 numbers whose product is $ac=
1(-12)=-12
$ and whose sum is $b=
-4
$ are $\left\{
-6,2
\right\}.$ Using these two numbers to decompose the middle term of the given trinomial, $
s^2-4st-12t^2
,$ then the factored form is
\begin{array}{l}
s^2-6st+2st-12t^2
\\\\=
(s^2-6st)+(2st-12t^2)
\\\\=
s(s-6t)+2t(s-6t)
\\\\=
s(s-6t)+2t(s-6t)
\\\\=
(s-6t)(s+2t)
.\end{array}