6. (20 points) A solid metal sphere of radius a = 5.5 cm has a net charge Qin = + 5 nC. The sphere is surrounded by a concentric conducting spherical shell of inner radius b = 9 cm and outer radius c = 12 cm. The shell has a net charge Qout = - 5 nC. A) What is Vc, the electric potential at the outer surface of the spherical shell, given the potential at infinity is zero? B) What is V0, the electric potential at the center of the metal sphere?