Two spherical shells have a common center. A -1.6 × 10-6 C charge is spread uniformly over the inner shell, which has a radius of 0.050 m. A +5.1 × 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 a distance (measured from the common center) of (a) 0.20 m, (b) 0.10 m, and (c) 0.025 m