Answer
$$ f^{-1}(x)=x^{\frac{3}{2}}$$
Work Step by Step
Given $$ y=x^{\frac{2}{3}} $$
Find the inverse:
\begin{aligned}
& y=x^{\frac{2}{3}}\\
& \Rightarrow x =y^{\frac{3}{2}} \ \ \ \\
&\text{Switch $ x $ and $ y $}\\
&y=x^{\frac{3}{2}}=f^{-1}(x)
\end{aligned}