The length of the deck ≥ 38.
The width is 29 feet, so double that (58) and you get two of the sides. subtract that from the perimeter you are looking for (134 - 58) and now you have what the remaining two sides must equal (76) divide that by two to get one side, which is also the length (38). The perimeter must be at least 134, but can be more, so the length has to be greater than or equal to 38.