A non-conducting solid sphere, of radius $$R$$, with its center at $$A$$, has a spherical cavity of diameter $$R$$ with center at $$B$$ as shown. There is no charge in the cavity while the solid part has a uniform volume charge density $$\rho$$. Electric potential at the center of the sphere, at point $$A$$, is $$V = \frac{k\rho R^2}{12\epsilon_0}$$ in SI units where the value of $$k$$ is

A

3

B

5

C

7

D

9