In cylindrical coordinates, which is what what the problem specifically asks you to use, the paraboloidal surface is . It should be easy to see that z is never more than 36. And you are told that z is not below 0.For each z, r goes from 0 to . Or you could argue that r goes from 0 to a largest value of 6 (where z= 0) and,for each r, z goes from 0 to .