Question

A small ball carrying - 2q charge is placed at the center of a spherical metal shell that carries charge +q

What is the charge of the inner and outer surfaces of the shell?

Answer 1

The charge of the inner surface of the shell: $0=-2q+x\to x=+2q$ ;

The charge of the outer surface of the shell: $+2q+x=+q\to x=-q$ .