Two known charges, -12.0 μC and 45.0 μC, and an unknown charge are located on the x axis. The charge -12.0 μC is at the origin, and the charge 45.0 μC is at x = 15.0 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. Is this situation possible? Is it possible in more than one way? Find the required location, magnitude, and sign of the unknown charge.