39. assignment (electric force)

Four charges (-5 microcoulombs, 5 microcoulombs, 5 microcoulombs, 10 microcoulombs) are located on the corners of a rectangle as shown in figure. The dimensions of the rectangle are L=60 cm W=15 cm. Calculate the magnitude and direction of the total electric force exerted on the charge at the lower left corner by the other three charges. 
Product description video:
https://youtu.be/5XV5qd1dja0