Required area $\begin{aligned}
& A=2\left[\int_0^2\left(3 \sqrt{y}-\frac{\sqrt{y}}{2}\right) d y\right]=2 \int_0^2 \frac{5 \sqrt{y}}{2} d y \
& =5\left[\frac{y^{3 / 2}}{3 / 2}\right]_0^2=\frac{10}{3}\left[2^{3 / 2}-0\right]=\frac{20 \sqrt{2}}{3}
\end{aligned}$ 