A point charge q is placed inside a conducting spherical shell of inner radius 2R and outer radius 3R at a distance of R from the centre of the shell. The electric potential at the centre of shell will be 14πϵ0 times.
5q6R
Induced charges will be −q and +q as shown in figure.
Potential at center will be V0=14πϵ0[qR−q2R+q3R]
=14πϵ0(5q6R)