Answer
$(y-12)(y-8)$
Work Step by Step
The 2 numbers whose product is $ac=
1(96)=96
$ and whose sum is $b=
-20
$ are $\left\{
-12,-8
\right\}.$ Using these two numbers to decompose the middle term of the given trinomial, $
y^2-20y+96
,$ then the factored form is
\begin{array}{l}
y^2-12y-8y+96
\\\\=
(y^2-12y)-(8y-96)
\\\\=
y(y-12)-8(y-12)
\\\\=
(y-12)(y-8)
.\end{array}