Find the magnetic flux density as a function of radius for the concentric hollow cylinders.
The currents are I(a) = 4 I and I(b) = -2I A
A positive current flows into the page.
Note: Can treat this as a hollow coaxial line. Current on the surface of inner conductor is 4I going into the page (positive current flows into the page) or is in negative z direction while current on outer conductor surface is 2I in the reverse direction or positive Z- direction. I is the general current. There is no third conductor.