Let S be the part of the sphere

x^2 + y^2 + z^2 = 25
that lies above the plane z = 4. Let S have constant density k.
(a) Find the center of mass.

(b) Find the moment of inertia about the z-axis.

so far I have found that the magnitude of r(theta)x r(thi)= 25sin(thi)but I cant figure out how to set up the integral to find the points for the center of mass