Answer
$n^2-10n+21$
Work Step by Step
Using the Distributive Property and then combining similar terms, the given expression, $
(n-3)(n-7)
,$ is equivalent to
\begin{array}{l}\require{cancel}
n(n)+n(-7)-3(n)-3(-7)
\\\\=
n^2-7n-3n+21
\\\\=
n^2-10n+21
.\end{array}