Answer:
We know that since it's a square, the lenght size is the same on all sides. We can simply use pythagoras theorem:
a^2 + a^2 = 13.5^2
13.5^2 = 182,25
182,25 : 2 (because there are 2 'a') = 91,125
<u>The square root of 91,125 is 9,55 feet.</u>