Consider a coaxial cable which consists of an inner wire of radius a surrounded by an outer shell of inner and outer radii b and c respectively. The inner wire carries an electric current `(i_0) and the outer shell carries an equal current in opposite direction. Find the magnetic field at a distance x from the axis where (a) xlta, (b) altxltb, (c) bltxltc and (d)xgtc. Assume that the current density is uniform in the inner wire and also uniform in the outer shell.