Answer
$7x^2(2x+3)$
Work Step by Step
Factoring the $GCF=
7x^2
,$ the given expression, $
14x^3+21x^2
,$ is equivalent to
\begin{array}{l}\require{cancel}
7x^2
\left(
\dfrac{14x^3}{7x^2}+\dfrac{21x^2}{7x^2}
\right)
\\\\=
7x^2(2x+3)
.\end{array}