3. [7 points] (Show all work) A metallic spherical shell has inner radius b and outer radius c. The net charge on the spherical shell is 20. A uniformly charged spherical insulator of radius a and total nonzero charge ( is al. the centre of the spherical shell. The system is in electrostatic equilibrium. a) What are the charges on the inner and outor surface of the spherical shell? - Q - Q outer smale b) Write an expression for the magnitude of the electric field E(r) in the following regions, () ra, illac