Answer
$20y^4-24y^3+12y^2$
Work Step by Step
Using $a(b+c)=ab+ac$ or the Distributive Property, the given expression, $
4y^2(5y^2-6y+3)
,$ is equivalent to
\begin{array}{l}\require{cancel}
4y^2(5y^2)+4y^2(-6y)+4y^2(3)
\\\\=
20y^4-24y^3+12y^2
.\end{array}