Answer
$\sqrt[5]{y^2} \text{ or } \left(\sqrt[5]{y}\right)^2$
Work Step by Step
We are asked to rewrite the exponent into radical form:
$y^{\frac{2}{5}}$
Recall the rational exponent property (pg. 382):
$a^{\frac{m}{n}}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$
Applying this property to our equation ($m=2$, $n=5$, $a=y$), we get:
$y^{\frac{2}{5}}=\sqrt[5]{y^2}=(\sqrt[5]{y})^2$