A hollow metal sphere has 7cm and 11cm inner and outer radii, respectively. The surface charge density on the inside surface is -200nC/m^2. The surface charge density on the exterior surface is +200nC/m^2 .
A.) What is the strength of the electric field at point 4 cm from the center?
B.) What is the strength of the electric field at point 12 cm from the center?