The force between two charged balls is 6.0 x 10-6 N. If we
double the distance and the charges on one ball, what's the
new force between the two charged balls? k= 9.0 x 10°
If you double the distance the force drops to a quarter so 6/4 x 10 ^-6 N. If you then double the charge on one ball, the force would double to 12/4 x 10^-6 = 3 x 10 ^-6 N