There is a hollow conducting spherical shell with an inner radius of 8 cm and an outer radius of 10 cm. A charge placed inside the inner surface of the shell causes an electric field at the inner surface of the shell, Ei, has a magnitude of 80 N/C and points toward the center of the sphere, and the electric field at the out surface, Eo, has a magnitude of 80 N/C and points away from the center of the sphere. Determine the magnitude of charge on the inner surface of the spherical shell.