Four charged particles are placed so that each particle is at the corner of a square. The sides of the square are 15 cm. The charge at the upper left corner is -3.0 µC, the charge at the upper right corner is -6.0 µC, the charge at the lower left corner is -2.4 µC, and the charge at the lower right corner is -9.0 µC. a. What is the net electric force on the +3.0 µC charge? b. What is the net electric force on the -6.0 µC charge? c. What is the net electric force on the -9.0 µC charge?