A 5.0 nC (nanno = 10-9) charge is at (0,0) and a -2.0 nC charge is at (3.0 m, 0). If the potential is taken to be zero at infinity, what is the electric potential energy of a 4.0 nC charge at point (0, 4.0 m)?

Uhh, I wish I could help, but I have no idea where to start