Three long wires are parallel to a z axis, and each carries a current of 10 A in the positive z direction their points of interaction with the xy plane from an equilateral triangle with sides of 50cm as shown in Figure. A fourth wire (wire b) passes through the mid point of the base of the triangle and is parallel to the other three wires. If the net magnetic force on wire a is zero, what are the

(a) Size and

(b) Direction (+z or -z) of the current in wireb?

L.