4 consider a square of charges where the side length of the square is

Question

4. Consider a square of charges, where the side length of the square is a = 0.8 m.At each corner of the square there is a different charge. At (0, 0), there is a 10nC charge. At (a, 0), there is a 6 nC charge. At (a, a), there is a-9 nC charge.Lastly, at (0, a) there is a -6 nC charge. Calculate the electric potential at (a/2, 0),in V. Use k = 9 x 109 N m2 / C2.