Reverse the order $of$ integration.

${\displaystyle \underset{0}{\overset{2}{}}}{\displaystyle \underset{x^2}{\overset{2x}{}}}f(x,y)dydx$

$\frac{{\displaystyle \underset{0}{\overset{4}{}}}{\displaystyle \underset{\frac{y}{2}}{\overset{\sqrt[\phantom{2}]{y}}{}}}f(x,y)dxdy}{{\displaystyle \underset{0}{\overset{2}{}}}{\displaystyle \underset{y}{\overset{\sqrt[\phantom{2}]{y}}{}}}f(x,y)dxdy}$

none $of$ these above

${\displaystyle \underset{0}{\overset{4}{}}}{\displaystyle \underset{y}{\overset{\sqrt[\phantom{2}]{y}}{}}}f(x,y)dxdy$