$($Figure $1)$is a cross section through three long wires with linear mass density$45$g$/$m$.$They each carry equal currents in the directions shown. The lower two wires are$4\mathrm{.}0$cm$$apart and are attached to a table. What current$$II$$will allow the upper wire to "float" so as to form an equilateral triangle with the lower wires? Express your answer with the appropriate units.