Answer
(a) The inner surface of the conductor has a charge of $+7~\mu C$
(b) The total charge on the outer surface of the conductor is $-11~\mu C$.
Work Step by Step
(a) There is no electric field inside a conductor. Therefore, the inner surface of the conductor must have a charge equal in magnitude and opposite in sign to the sum of the two charges $q_1$ and $q_2$. The inner surface of the conductor has a charge of $+7~\mu C$
(b) Since the total charge of the conductor is $-4~\mu C$, the total charge on the outer surface of the conductor is $-11~\mu C$.
