Gravitational force is given by the following formula:
F = GMm/r^2
Where;
F = Gravitational force, G = Gravitational constant, M & m = masses of two bodies which are constant in this case, and r = distance between the masses.
It can be seen that F α 1/r^2.
Therefore, the far the two masses are from each other, the smaller the gravitational force and vice versa.
It is indicated that:
AB = 300 km
BC = 400 km
CA = 100 km
Therefore,
gravitational force will largest between C and A due to smaller distance between them.