A charge of total amount $$Q$$ is distributed over two concentric hollow spheres of radii $$r$$ and $$R\ (R > r)$$ such that the surface charge densities on the two spheres are equal. The electric potential at the common centre is

A

$$\frac{1}{4\pi\varepsilon_0}\cdot\frac{(R-r)Q}{(R^2+r^2)}$$

B

$$\frac{1}{4\pi\varepsilon_0}\cdot\frac{(R+r)Q}{2(R^2+r^2)}$$

C

$$\frac{1}{4\pi\varepsilon_0}\cdot\frac{(R+r)Q}{(R^2+r^2)}$$

D

$$\frac{1}{4\pi\varepsilon_0}\cdot\frac{(R-r)Q}{2(R^2+r^2)}$$