Consider a pair of long coaxial cylindrical conductors centered on the z-axis. A current I flows in the +z-direction in the inner conductor, and returns in the outer conductor. The radius of the inner conductor is a, and the outer conductor has inner radius b and outer radius c. The current is uniformly distributed within each conductor. Determine the magnetic flux density B(r) for all four regions (inside the inner conductor, between the conductors, inside the outer conductor, and outside everything.).