Answer
$d=60\sqrt{2}\approx84.85281374\text{ ft}$
Work Step by Step
The diagonal of the square is the hypotenuse of a right-angled triangle, thus the distance can be calculated using the Pythagorean Theorem.
$d^2=a^2+b^2\\
d^2=60^2+60^2\\
d^2=2(60^2)\\
d=\sqrt{2(60^2)}$
$d=60\sqrt{2}\approx84.85281374$ feet
