Two straight wires, traversed by currents i1=5 A and i2, are arranged in the space so that they are parallel to each other at a constant distance d=15cm. At a point P in space at a distance d from both i wires a magnetic field is observed perpendicular to the plane of the wires. Determine: a) the current i2 and its direction with respect to the current i1; b) the modulus of the magnetic field in P; c) the force (module, direction e direction) per unit of length acting on each thread.