The length of the diagonal of the square is 22.05 units
A square have all its sides equal to each other.
Therefore, using Pythagoras theorem,
c² = a² + b²
c² = (9√3)² + (9√3)²
c² = 81 × 3 + 81 × 3
c² = 243 + 243
c² = 486
square root both sides
c = √486
c = 22.045407685
c = 22.05 units
learn more on square here: https://brainly.com/question/2292568?referrer=searchResults
#SPJ1