Four charges are arranged in a square with sides of length 2.5cm. The two charges in the top right and bottom left corners are +3.0μC. The charges in the other two corners are -3.0μC. What is the net force exerted on the charge in the top right corner by the other three charges?

Answer 1

apply Coulomb's law to each charge and add them up.
There are many similar problems worked online.
Post your work if you get stuck.