Answer
$B_{}=75.4nT.$
Work Step by Step
Using Formula, $A=\pi R^2$,
$
\begin{aligned}
B & =\frac{\mu_0 i_d r}{2 \pi R^2}=\frac{\mu_0 J_d A r}{2 \pi R^2}=\frac{\mu_0 J_d\left(\pi R^2\right) r}{2 \pi R^2}=\frac{1}{2} \mu_0 J_d r \\
& =\frac{1}{2}\left(4 \pi \times 10^{-7} \mathrm{~T} \cdot \mathrm{m} / \mathrm{A}\right)\left(6.00 \mathrm{~A} / \mathrm{m}^2\right)(0.0200 \mathrm{~m})\\&=75.4 \mathrm{nT} .
\end{aligned}
$
