Two current-carrying wires are exactly parallel to one another and both carry 3.5 A of current. The two wires are separated by a distance of 15 cm. The current in wire 1 moves down and the current in wire 2 also moves down. What is the magnitude of the magnetic force per unit length caused by wire 1 on wire 2? What is the direction of the magnetic force caused by wire 2 on wire 1?