Interior to the Earth, the Gravitational Attraction Varies Directly as the Distance

Multiple Choice

Interior to the Earth, the gravitational attraction varies directly as the distance from the centre of the Earth. What is the work necessary to lift a mass weighing 1 kg at the surface from the centre to the surface? Assume that the radius of the Earth is 6,400 km and the force of attraction of the Earth on a mass at its surface is 9.8 Newtons.

A) 24,260 N . km
B) 31,360 N . km
C) 36,480 N . km
D) 42,400 N . km
E) none of the above