Two Long, Parallel Wires Are Spaced 1 M Apart in Air

Two long, parallel wires are spaced 1 m apart in air, and you have established a current of 1 A in each. The force per unit length that each wire exerts on the other is

A) 4 $\pi$ µ_{0 .}
B) 2 $\pi$ µ_{0 .}
C) µ_{0 .}
D) µ₀/4 $\pi$
E) µ₀/2 $\pi$