Solution to task 412 from Chertov´s for extramural stud

Solution to task 412 from Chertov´s for extramural stud

412. On three parallel straight wires, located at the same distance d = 20cm from each other, the same currents I = 400 A flow. In the two wires, the directions of the currents coincide. Calculate for each of the wires the ratio of the force acting on it to its length.