A point charge of -7pC is concentric with two spherical conducting thick shells, as show in the figure below.

A point charge of -7pC is concentric with two spherical conducting thick shells, as show in the figure below. The smaller spherical conducting shell has a net charge of -22 pC 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, 2.8cm from the -7pC point charge? Under static conditions, the charge on a conductor resides on the surface of the conductor.