EXPLANATION
The answer is 127.3 feet
Let's see the facts:
The square has sides of 90 feet. We can use theb 45-45-90 triangle property that says that it has one right angle, and two other angles are equal to 45 degrees. So both legs are equal and the length of the hypotenuse is sqrt(2) times the length of a leg.
The diagonal is gievn by applying the Pythagorean Theorem as shown as follows:
Simplifying: