A point charge of -5pC is concentric with two spherical conducting thick shells, as show in the figure below.

A point charge of -5pC is concentric with two spherical conducting thick shells, as show in the figure below. The smaller spherical conducting shell has a net charge of 21pC and the larger spherical conducting shell has a net charge of -12pC. What is the charge on the inner surface of the small spherical conducting shell, 1cm from the -5pC point charge? Under static conditions, the charge on a conductor resides on the surface of the conductor.