length (l) =54
breath (b) =72
l²+b²= diagonal²..........(Pythagoras theorem) and (all sides of rectangle are 90degree)
(54)²+(72)²=diagonal²
2916+5184=diagonal²
8100=diagonal²
90= diagonal.............(taking square root)
length of diagonal is 90ft
i hope it helps
have a nice day and thanks for asking this question