The Figure Shows a Cross Section of Three Parallel Wires

Multiple Choice

The figure shows a cross section of three parallel wires each carrying a current of 15 A.The currents in wires A and C are out of the paper,while that in wire B is into the paper.If the distance R = 5.0 mm,what is the magnitude of the force on a 4.0-m length of wire C?

A) 90 mN
B) 54 mN
C) 30 mN
D) 18 mN
E) 36 mN