Dear Student,
The above problem can be solved by determining the gravitational potential at the initial point (r = R/2 from the centre of the earth) and the final point (r = 2R from the centre of the earth.
Assuming the earth to be a sphere of uniform mass density.
Gravitational potential at any point above the surface, i.e. , r > R is

For an interior point (r < R), the gravitational potential can be determined as:

Change in V(r) from r = R/2 to r = 2R:

Ans (c)

Regards