In the figure, four long straight wires are perpendicular to the page, and their cross sections form a square of edge lengtha = 15.5 cm. Each wire carries 4.00 A, and the currents are out of the page in wires 1 and 4 and into the pagein wires 2 and 3. In unit-vector notation, what is the net magneticforce per meter of wire length on wire 4?