Two long conductors, separated by a distance d carry currents `I_1 and I_2` in the same direction. They exert a force F on each other. Now, the current in one of them is increased to two times and its direction is reversed. The distance is also increased to `3d`. The new value of the force between them is
Options:
(a) `-F/3`
(b) `F/3`
(c) `(2F)/3`
(d) `(-2F)/3`