Answer
$48\bar{0},000\ ft$
Work Step by Step
Using the Pythagorean Theorem, we have:
$${a}^2+{b}^2 = {c}^2.$$
Then
$$
b = \sqrt{c^2-a^2}= \sqrt{521000^2-203000^2}=479824.96\ ft \approx 48\bar{0},000\ ft
.$$
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