A long, cylindrical conductor of radius R carries a current I as shown in the figure below. The current density J, however, is not uniform over the cross-section of the conductor but is a function of the radius according to J = 6br^4, where b is a constant.

Find an expression for the magnetic field magnitude B at the following distances, measured from the axis. (Use any variable or symbol stated above along with the following as necessary: μ0.)
(a) r1 < R
B = ?
(b) r2 > R
B = ?