A coaxial cable consists of a solid inner cylindrical conductor of radius 1.00 mm and an outer cylindrical shell conductor of inner radius 2.00 mm and outer radius 3.00 mm. There is a current of 18 A down the inner wire and an equal return current in the outer conductor. The currents are uniform over the cross section of each conductor. Find the numerical value of ∫CB • dℓ for a closed circular path (centered on the axis of the cable and in a plane perpendicular to the axis) which has a radius r for

(a) r = 1.50 mm,

(b) r = 2.50 mm, and

(c) r = 3.50 mm.