An insulating sphere with radius R rotates with angular velocity = z. The total charge Q

An insulating sphere with radius R rotates with angular velocity ω = ωẑ. The total charge Q of the sphere is uniformly distributed over its surface.

(a) Show that the magnetic field outside the insulating sphere is identical to the magnetic field outside a uniformly magnetized sphere of radius R when the magnetization M = Mẑ and M are suitably chosen.
(b) Use the result of part (a) to find the magnetic moment of the insulating sphere.