Point charge 1.5{\rm \mu C} is located at x = 0, y = 0.30 {\rm m}, point charge -1.5{\rm \mu C} is located at x = 0 y = -0.30 {\rm m}. What are (a)the magnitude and (b)direction of the total electric force that these charges exert on a third point charge Q = 4.5{\rm \mu C} at x = 0.40 {\rm m}, y = 0?