Answer
$7.5\ mi$
Work Step by Step
Step 1. Using the figure in the exercise and the given quantities, we have the angle
$C=180^\circ-51^\circ-48^\circ=81^\circ$
Step 2. Using the Law of Sines, we have
$\frac{sin48^\circ}{b}=\frac{sin81^\circ}{10}$
Thus
$b=\frac{10sin48^\circ}{sin81^\circ}\approx7.5\ mi$
