Answer: The length of the given rectangle is 51 feet.
Step-by-step explanation: Given that the ratio of length to width in a rectangle is 3 to 1 and the perimeter of the rectangle is 136 feet.
We are to find the length of the rectangle.
Let the length and breadth of the rectangle be 3x feet and 1x feet respectively.
Then, according to the given information, we have

Therefore, width = 17 feet and length = 17 × 3 = 51 feet.
Thus, the length of the given rectangle is 51 feet.