Three charges are arranged at the vertices of an equilateral triangle with sides of length 0.06 meters. The charge at the first vertex (top point of triangle) is -5.0 μC. The charge at the bottom left vertex is 4.0 μC. The charge at the bottom right vertex is 7.0 μC.
How much Electrical Potential Energy is stored in the equilateral triangle? (The answer is -405 Joules, but I can't figure out how to get that).