the length of the diagonal of the deck can solved using the pythagorean theorem because the diagonal the sides of a rectangle will form a right triangle. pythagorean theorem states that
C^2 = B^2 + A^2
where C is the hypotenuse or the diagonal of the rectangles
B and A are the sides of the rectangle
C^2 = 10^2 + 23^3
C^2 = 629
C = 25.08 ft