Pyhsics
posted by Cookie .
The force of repulsion that two like charges exert on each other is 3.0 N. What will the force be if the distance between the charges is increased to 3 times its original value?

You must have been told that the electrostatic force between two charges varies inversely with the square of the distance between them. That means, in this case, that the force gets multiplied by a factor 1/3^2 = 1/9.