Answer
$B=3.3\mu T$
Work Step by Step
To find the magnetic field at a certain radius from a wire, use Formula 29-4 on pg. 837 $$B=\frac{\mu_o i}{2\pi R}$$ Substitute known values of $i=100A$, $\mu_o=4\pi \times 10^{-7} H/m$, and $R=6.1m$ yields a magnetic field of $$B=\frac{(4\pi \times 10^{-7} H/m)(100A)}{2\pi(6.1m)}=3.3\times 10^{-6} T=3.3\mu T$$
