Answer
$\dfrac{\sqrt{21xy}}{3y}$
Work Step by Step
Rationallizing the denominator of $
\sqrt{\dfrac{7x}{3y}}
$ results to
\begin{array}{l}
\sqrt{\dfrac{7x}{3y}\cdot\dfrac{3y}{3y}}
\\\\=
\sqrt{\dfrac{21xy}{9y^2}}
\\\\=
\dfrac{\sqrt{21xy}}{3y}
.\end{array}
