The current density inside a long, solid, cylindrical wire of radius $a=3\mathrm{.}4mm$ is in the direction of the central axis and its magnitude varies linearly with radial distance $r$ from the axis according to $J=J_0\frac{r}{a},$ where $J_0=170\frac{A}{m^2}.$ Find the magnitude of the magnetic field at a distance $($a$)r=0,($b$)r=2\mathrm{.}4mm$ and $(c)r=3\mathrm{.}4mm$ from the center.

$($a$)$ Number

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$($b$)$ Number

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$($c$)$ Number

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