A point particle that has a charge of 18.0 µC is located at x = 0, y = 0 and a point particle that has a charge q is located at x = 14.4 cm, y = 0. The electric force on a point particle that has a charge of 7.2 µC at x = 28.8 cm, y = 0 is -(19.7) N . Determine the charge q.