let the diagonal be a.
now, as we know that each angle in a rectangle is right angle.
thus we have a right angled triangle.
now, we can apply pythagoras theorum.
a^2 = 54^2 + 72^2
= 2916 + 5184
=8100
thus, a^2 = 8100
thus, a = 90.
Thus the diagonal is 90metres
