Electrostatic Potential (Charged Sphere)

A unit positive point charge is taken slowly through an infinitesimally thin tube inside a charged dielectric sphere of radius R having uniform positive charge density rho. The initial and final positions of the charge are marked by A and B at distances 2R and 3R respectively from the centre of the sphere. In this process, the magnitude of the total work done on the point charge is rho R^2/(n epsilon_0). The value of n is: (epsilon_0 is the permittivity of vacuum)