Diagonal measure of 28ft x 28ft square?

Square of the hypotenuse is equal to the sum of the squares of the other 2 sides. Therefore 28*28 + 28*28 =784+784 =1568. Square root 1568 = 39.598ft or 39ft 6and 17-20ths inches. Or just over 39ft 6and threequarters inches.