Two straight and parallel wires carry a current. What distance must separate the two of them?

Two straight and parallel wires of length 1.0 m carry a current - the first carries a currecnt of 9.0 A while the other wire carries a current of 4.0 A. What distance must separate the two straight and parallel copper wires if the force between them is to be 6.0 x 10^-6 N?