Answer
$\dfrac{3y}{\sqrt[3]{21y^2}}$
Work Step by Step
Rationalizing the numerator of $
\sqrt[3]{\dfrac{9y}{7}}
$ results to
\begin{array}{l}
\sqrt[3]{\dfrac{9y}{7}}
\cdot
\sqrt[3]{\dfrac{3y^2}{3y^2}}
\\\\=
\sqrt[3]{\dfrac{27y^3}{21y^2}}
\\\\=
\dfrac{3y}{\sqrt[3]{21y^2}}
.\end{array}