Answer
We can rank the arrangements according to the magnitude of the net force on wire A due to the currents in the other wires:
$1 \gt 3 \gt 2$
Work Step by Step
We can write an expression for the force on a current-carrying wire due to another current-carrying wire:
$F = \frac{\mu_0~L~i_1~i_2}{2\pi~d}$
According to the text on page 854: "Parallel wires carrying currents in the same direction attract each other, whereas parallel wires carrying currents in opposite directions repel each other."
We can consider the net force on wire A in each situation:
(1) The forces due to the other two wires is directed to the left.
$F_{net} = \frac{\mu_0~L~i^2}{2\pi~d}+\frac{\mu_0~L~i^2}{2\pi~D}$
(2) The force due to the closer wire is directed to the right while the force due to the farther wire is directed to the left.
$F_{net} = \frac{\mu_0~L~i^2}{2\pi~d}-\frac{\mu_0~L~i^2}{2\pi~D}$
(3) The force due to the closer wire is directed upward while the force due to the farther wire is directed to the left.
$F_{net} = \sqrt{(\frac{\mu_0~L~i^2}{2\pi~d})^2+(\frac{\mu_0~L~i^2}{2\pi~D}})^2$
$\frac{\mu_0~L~i^2}{2\pi~d} \lt F_{net} \lt \frac{\mu_0~L~i^2}{2\pi~d}+\frac{\mu_0~L~i^2}{2\pi~D}$
We can rank the arrangements according to the magnitude of the net force on wire A due to the currents in the other wires:
$1 \gt 3 \gt 2$
