Answer
a) $B=1.285\times 10^{-3}T$
b) $\frac{F}{L}=290\frac{N}{m}$
Work Step by Step
(a) We know that
$B=\frac{\mu_{\circ}I}{2\pi r}$
We plug in the known values to obtain:
$B=\frac{(4\pi \times 10^{-7})(255\times 10^3)}{2\pi(35)}$
$B=1.285\times 10^{-3}T$
(b) As $\frac{F}{L}=\frac{\mu_{\circ}I_1I_2}{2\pi d}$
We plug in the known values to obtain:
$\frac{F}{L}=\frac{4\pi \times 10^{-7}(255\times 10^3)^2}{2\pi(35)}$
$\frac{F}{L}=290\frac{N}{m}$