A spherical hollow cavity is made in a lead sphere of radius `R` such that is 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 distacne d from the centre of the lead sphere on the straight line connecting the centeres of the spheres and that of the hollow if `d =2R`
.
A. `(7GMm)/(18R^(2))`
B. `(7GMm)/(36R^(2))`
C. `(7GMm)/(9R^(2))`
D. `(7GMm)/(72R^(2))`
