#### Answer

$\sqrt[3]{0.21y^2}$

#### Work Step by Step

Using $\sqrt[a]{x}\sqrt[a]{y}=\sqrt[a]{xy}$, the given expression, $
\sqrt[3]{0.7y}\sqrt[3]{0.3y}
,$ simplifies to
\begin{array}{l}\require{cancel}
\sqrt[3]{0.7y(0.3y)}
\\\\=
\sqrt[3]{0.21y^2}
.\end{array}