Two spherical shells have a common center. A -3.00 x10-6 C charge is spread uniformly over the inner shell, which has a radius of 0.050 m. A +6.00 x10-6 C charge is spread uniformly over the outer shell, which has a radius of 0.15 m. Find the magnitude and direction of the electric field at a distance (measured from the common center) of:
(a) 0.20 m