Answer
$\sqrt[5]{y^6} \text{ or } \left(\sqrt[5]{y}\right)^6$
Work Step by Step
Note that:
$y^{1.2} = y^{\frac{6}{5}}$
Recall the rational exponent property (pg. 382):
$a^{\frac{m}{n}}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$
Applying this property ($m=6$, $n=5$, $a=y$), we get:
$y^{\frac{6}{5}}=\sqrt[5]{y^6}=\left(\sqrt[5]{y}\right)^6$