Concentric shells r = 20 cm and r = 30 cm are held at V = 0 and V = 50, respectively. If the space between them is filled with dielectric material (ε = 3.1ε0, a = 10–12 S/m), find:

(a) V, E, and D,

(b) The charge densities on the shells,

(c) The leakage resistance.