Evaluate the triple integral by transforming to spherical coordinates.

Question

Evaluate the integral by transforming to spherical coordinates $ \iiint_S [(x-a)^2 + (y-b)^2 + (z-c)^2]^{\frac{-1}{2}} dxdydz$ , where S is a solid sphere of radius R and centre at origin, and $(a,b,c)$ is a fixed point outside this sphere. I tried via spherical coordinates but it's going too complicated.