Three parallel current-carrying wires are shown in figure. The currents in each wire are I1 = 0.5 A, I2 = 0.75 A, I3 = 0.25 A. If the wires are separated by distances r1 = 0.185 m and r2 = 0.29 m. What is the net magnetic force per unit length on the middle wire due to other wires?