A solid insulating sphere of radius \(R\) has a non-uniform volume charge density given by \(\rho(r) = Cr\) for \(r \le R\), where \(C\) is a positive constant and \(r\) is the radial distance from the center of the sphere. The electric potential is defined to be zero at infinity (\(V(\infty) = 0\)). Which of the following expressions represents the electric potential \(V(r)\) inside the sphere as a function of \(r\) for \(r \le R\)?