i'm struggling with this question bad. i'm not sure what i'm doing wrong. thank you!

Problem 4 A portion of a long, cylindrical coaxial cable is shown in the following figure. A current I flows down the center conductor, and this current is returned in the outer conductor. Determine the magnetic field in the regions: a. ) r Er1 b.) 12 2 r 2 71 C.) 73 27 2 12 d. ) r 2 73 Assume that the current is distributed uniformly over the cross sections of the two parts of the cable. 13