Four charges are placed at the four corners of a square of side 15 cm. The charges on the upper left and right corners are +3 C and -6 C respectively....

Four charges are placed at the four corners of a square of side 15 cm. The charges on the upper left and right corners are +3 μC and -6 μC respectively. The charges on the lower left and right corners are -2.4 μC and -9 μC respectively. The net electric force on -9 μC charge is:

18 N, 750 below the positive x-axis

18 N, 750 below the negative x- axis

18 N, 750 above the negative x- axis

18 N, 750 above the positive x- axis