Two very long straight parallel wires carry steady currents `i` and `2i` in opposite directions. The distance between the wires is `d`. At a certain instant of time a point charge `q` is at a point equidistant from the two wires in the plane of the wires. Its instantaneous velocity `vecv` is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on t he charge at this instant is