The shortest side is 20 feet, the second side is 24 feet and the third side is 36 feet.
Step-by-step explanation:
Assuming that the shortest side of this triangle has a length of "x" feet, then one side is "x + 4" feet and the third is "2*x - 4" feet. Since the perimeter of the deck is 80 feet, then the sum of the length of these sides should be equal to that.
The shortest side is 20 feet, the second side is 24 feet and the third side is 36 feet.