Answer
$12n^4-16n^3-20n^2+40n$
Work Step by Step
Using $a(b+c)=ab+ac$ or the Distributive Property, the given expression, $
4n(3n^3-4n^2-5n+10)
$, is equivalent to
\begin{array}{l}\require{cancel}
4n(3n^3)+4n(-4n^2)+4n(-5n)+4n(10)
\\\\=
12n^4-16n^3-20n^2+40n
.\end{array}