r = sqrt(x^2 + y^2 + z^2)
theta = arctan(y/x)
phi = arccos(z/r)
(Integral from 0 to pi/2) (Integral from 0 to sqrt(9-y^2)) (Integral from sqrt(x^2+y^2) to sqrt(18-x^2-y^2)) (x^2 + y^2 + z^2)
r = sqrt(9-y^2)
theta = arctan(y/x)
phi = arccos(z/r)by changing to spherical coordinates.