Answer
The net magnetic force on wire 3 due to the currents in the other wires is $~~0$
Work Step by Step
We can write the general expression for the magnetic force on a current-carrying wire due to a parallel current-carrying wire:
$F = \frac{\mu_0~L~i_1~i_2}{2\pi~d}$
Note that currents in the same direction attract each other.
The force on wire 3 due to the currents in wire 1 and wire 2 is directed in the -y direction.
The force on wire 3 due to the currents in wire 4 and wire 5 is directed in the +y direction.
By symmetry, the net magnetic force on wire 3 due to the currents in the other wires is $~~0$
