This a problem which was assigned using webassign: Two known charges, -10.4 µC and 46.4 µC, and an unknown charge are located on the x axis. The charge -10.4 µC is at the origin, and the charge 46.4 µC is at x = 15.6 cm. The unknown charge is to be placed so that each charge is in equilibrium under the action of the electric forces exerted by the other two charges. Find the required location and magnitude of the unknown charge. I got -0.0497 cm for part 1 of the question(which webassign says is wrong). I don't know how to answer part two the question.