A pair of long, parallel wires, wire 1 and wire 2, are carrying currents I1 and I2 respectively. The vector force per unit length of wire 1 on wire 2 is f0. If the distance between them is changed by a factor of 1.3 and the current in one of the wires wires is reversed and changes in magnitude by a factor of 1.8, what is the new force per unit length, fnew, in terms of the original force per unit length, f0? Supply the missing numerical factor below.