Placing object between two charged sphere to have no electric net force

In this video, we tackled a problem regarding electrostatic force. The problem was as follows:
Two small spheres, with charges 1.6 * 10^-5 C and 6.4 * 10^-5 C, are situated 2.0 m apart. They have the same sign. Where, relative to these two objects, should a third object be situated, of the opposite sign and whose charge is 3.0*10^-6 C, so that it experiences no net electrical force? Do we really need to know the charge or sign of the third object?