Two charges attract each other with a force of 3.0 n. what will be the force if the distance between them is reduced to one-ninth of its original value?

The electrostatic force between two charges is given by

where ke is the Coulomb's constant, q1 and q2 are the two charges and d is the distance between the two charges.
We can see from the formula that the force is proportional to . This means that if we reduce the distance to one-ninth, i.e. the new distance is

then the force will scale as
 
So, the new force will be 81 times stronger than the initial value, therefore the new force is

Ibelieve the answer is d. densityhope my answer has you : )