Problem #$3($Show work to get credit$)(40$ Points$)$

A long cylindrical conductor of radius R carries a current I as shown below. The current density J $,$ however, is not uniform over the cross section of the conductor but rather is a function of the radius according to $J=b{r}^2,$ where b is a constant. Find an expression for the magnetic field magnitude $B(a)$ at a distance $r_2>R{r}_1(20$ Points$)$ and $(b)at$ a distance $r_2>R$ measured from the center $of$ the conductor. $(20$ Points$)$