28. Sphere A has a mass of 100 kg. It is 50 m away from sphere B, which has a mass of 25 kg. The force between them is F. The distance between them is halved and the mass of sphere A stays the same. What does the mass of sphere B have to be in order for the force to stay the same? (1) 6.25 kg (2) 12.50 kg (3) 31.25 kg (4) 50.00 kg​