Hello everyone. I'm having troubles getting the last part of this question. An isolated conductor of arbitreary shape has a net charge of +10x10^-6C. Inside the conductor is a cavity within which is a point charge q = +3.0x10^-6C. What is the charge (a) on the cavity wall and (b) on the outer surface of the conductor? I got (a) which is -3.0x10^-6C because the charge insdie a conductor has to be 0. But (b) is +1.3x10^-5C. I have no idea how they came up with this.