Answer
$x\sqrt[3]{21}$
Work Step by Step
Using the properties of radicals, the given expression, $
\sqrt[3]{7x}\sqrt[3]{3x^2}
,$ simplifies to
\begin{array}{l}\require{cancel}
\sqrt[3]{7x(3x^2)}
\\\\=
\sqrt[3]{21x^3}
\\\\=
\sqrt[3]{x^3\cdot21}
\\\\=
\sqrt[3]{(x)^3\cdot21}
\\\\=
x\sqrt[3]{21}
\end{array}