Two charges are located on the x axis: q1 = +6.0 µC at x1 = +4.0 cm, and q2 = +6.0 µC at x2 = -4.0 cm. Two other charges are located on the y axis: q3 = +4.0 µC at y3 = +5.0 cm, and q4 = -7.0 µC at y4 = +7.0 cm. Find the net electric field (magnitude and direction) at the origin.