Two equal positive charges of magnitude q1 = q2 = 6 nC are on the y axis at y1 = +3 cm and y2 = -3 cm. (a) What is the magnitude and direction of the electric field on the x axis at x = 6 cm? b) What is the force exerted on a third charge q0 = 4 nC when it is placed on the x axis at x = 6 cm?