Answer
$55.2~mi$
Work Step by Step
Using the Pythagorean Theorem, we can plug in our variable and then solve:
$${a}^2+{b}^2 = {c}^2$$
$${29}^2+{47}^2 = {c}^2$$
Rearranging gives
$${a} = \sqrt{{47}^2+{29}^2}$$
The answer, to 3 significant digits is
$$c = 55.2$$
