Two spherical shells have a common center. A -2.5 10-6 C charge is spread uniformly over the inner shell, which has a radius of 0.050 m. A +4.1 10-6 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 the following distances (measured from the common center).
(a) 0.20 m magnitude
(b) 0.10 m magnitude
(c) 0.025 m magnitude