To place caution tape across both diagonals of the broken rectangular door, you'll be forming an "X" shape. Each diagonal is equal to the hypotenuse of a right triangle with legs of 3 feet and 7 feet. You can use the Pythagorean theorem to find the length of each diagonal:
Diagonal = √(3^2 + 7^2)
Diagonal = √(9 + 49)
Diagonal = √58 feet
For both diagonals, you would need 2 times the length of one diagonal:
Total caution tape needed = 2 * √58 feet ≈ 15.16 feet.
So, Martin will need approximately 15.16 feet of caution tape to place across both diagonals of the broken door.