Two Parallel Long Wires Carry the Same Current and Repel

Multiple Choice

Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these currents are doubled and the wire separation tripled, the force per unit length becomes:

A) 2F/9
B) 4F/9
C) 2F/3
D) 4F/3
E) 6F