The gravitational force between two objects varies inversely with the square of the distance between them.
So if the distance is multiplied by a factor of 5, the force is multiplied by a factor of (1/5²).
New force = (50 Newtons) x (1/5²)
New force = (50 / 5²) Newtons
New force = (50 / 25) Newtons
New force = 2 Newtons (A)