(b) Consider a coaxial cable, shown in the Figure, that consists of a cylindrical conductor of radius r, enclosed in a cylindrical shell, of inner radius rz and outer radius

r3. A current I flows from left to right in the inner conductor, while a current of same amount I flows from right to left in the outer conductor. You may assume that the current density within each conductor is uniform. Determine the magnetic field in the regions r 73.