Find position, magnitude, and direction

[wayneinsane]

Homework Statement

Three long wires( 1,2 and 3) are coplanar and hang vertically. The distance between wire 1 and 2 is 20 cm. On the left wire 1 carries an upward current of 1.5 A. To the right the wire 2 carries a downward current of 4 A. Wire 3 is located such that, when it carries certain current such that no net magnetic force acts upon any of the wires. Find the position of wire 3 and the magnitude and direction of the current in 3.

Homework Equations

Ummm...?

The Attempt at a Solution

I'm drawing a blank...This question confuses me.

 

[danago]

What is the magnetic field at a distance 'r' produced by an infinitely long wire with current 'I'?