The force between two charges is inversely proportional to the square of the distance between them. This means that if the distance between the charges is increased by a factor of 2, the force between them will decrease by a factor of 2^2 = 4.
In this case, if the distance between the charges is increased by 8, the force between them will decrease by a factor of (8)^2 = 64. Therefore, the force between the charges will decrease significantly if the distance between them is increased by 8. There