Express the integral as an equivalent integral with the order of integration reversed:

$[5$ points each$]$

a$){\displaystyle \underset{0}{\overset{1}{}}}{\displaystyle \underset{x^2}{\overset{\sqrt[\phantom{2}]{x}}{}}}f(x,y)dydx$

b$){\displaystyle \underset{0}{\overset{2}{}}}{\displaystyle \underset{x^3}{\overset{4x}{}}}f(x,y)dydx$