Assuming that the 40 and 30 refer to sides of a rectangle and not to any of the infinite number of other possible shapes, the answer is 50.
A square with a 30-inch diagonal measurement has sides of 21.21 inches in length.
The diagonal length is about 20.59
Sqrt(282 + 402) = a whisker under 48 ft 10 in
67'1"
The square has a diagonal measurement of: 1.13 km
32.311
A square with a 30-inch diagonal measurement has sides of 21.21 inches in length.
Using Pythagoras the diagonal is 20 times square root of 2
46.648 ft
That would be 34 feet.
The diagonal measurement of an 8 ft square is: 11.31 feet.
The diagonal length is about 20.59
Since the rectangle has right angles, you can use Pythagoras' Theorem in this case.
The diagonal is 20.
The diagonal measurement for 36 feet by 36 feet is 50.91 feet.
A 12" x 12" square has a diagonal measurement of: 16.97 inches.
Use Pythagoras' theorem:- 502+302 = 3400 and the square root of this is the length of the diagonal which is about 58.309 feet to 3 dp