Answer
Approximation: $D = 40mi$
Actual: $D = 40.78mi$
Work Step by Step
$D=\sqrt{2*3960mi*1135ft*{1135ft}^{2}}$
$D=\sqrt{2*3960mi*0.21mi*{0.21mi}^{2}}$
This is really time-consuming, but its solvable
$D=\sqrt{1603.2mi}$
Now, let us get an approximation of the square root of 1603.2:
$\sqrt{1603.2}$
$= \sqrt{16032 * \frac{1}{10}}$
$= \sqrt{1002 * 16 * \frac{1}{10}}$
$=4\sqrt{1002 * \frac{1}{10}}$
$=4\sqrt{10.02 * 100 * \frac{1}{10}}$
$=40\sqrt{10.02 * \frac{1}{10}}$
$=40\sqrt{10.02 * \frac{1}{10}}$
$=40\sqrt{1.002}$
Claim this answer if I am wrong, but since the square root of 1.002 is basically just 1 (and since we have to answer in the least number of sig. figures, we may leave it at 40)
$D=40$
