Electrostatic repulsion is the force between two charges having the same sign, that tends to separate them further. The force is proportional to the product of the charges, and inversely proportional to the square of the distance between them.
Answer: the answer should be 6,720 decameters.
The answer would be c because a surface wave travels between two different materials, like air and water.
We do not feel the gravitational forces from objects other than the Earth because they are weak.
