A spherical hollow cavity is made in a lead sphere of radius R, such that its surface touches the outside surface of the lead sphere and passes through its centre. The mass of the sphere before hollowing was M. With what gravitational force will the hollowed out lead sphere attract a small sphere of mass 'm', which lies at a distance d from the centre of the lead sphere on the straight line connecting the centres of the sphere and that of hollow, if d=2R:
(A) 7GMm/18R2 (B) 7GMm/36R2 (C) 7GMm/9R2 (D) 7GMm/72R2
