This is a parabola in the XY plane and your bounds are given. So lets set this up
Where does this come from? Well we are bounded by the x function and the co-ordinate planes. So clearly, our dx integral is from 0-->function. Likewise, y is bounded by the co-ordinate axis and a function, but in this case that function is 3. Thus our bounds are from 0-->3
You can also switch the limits of integration here and compute dy first before dx.