I know the answer already, I just want to know how to solve it.
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Added: Look at both curves as functions of the form $\,x(y)\,$. Draw a diagram if necessary and find out where they meet.
The function $\,x=2y\,$ is above the function $\,x=y^2\,$ on $\,y\in [0,2]\,$ , i.e. $\,2y\geq y^2\,\,,\forall\,y\in [0,2]\,$ , so the volume of revolution is Pi times the integral on the given interval of the difference of squares of the given functions.