A charged metallic sphere A of radius 1 cm is suspended by a nylon thread. Another charged metallic sphere B, carried by an insulating handle, is brought closer to A to a distance of 9.0 cm between their centers. The resulting repulsion between the two spheres is F. Then, the spheres A and B are touched by two uncharged spheres C and D respectively. C and D are then removed and B is brought closer to A to a distance of 4.5 cm between their centers. All the spheres are identical.The new repulsive force between the spheres A and B is

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