Answer:
The length of the pipe = 17 feet
Step-by-step explanation:
length = 15 feet
width = 8 feet
Pythagorean theorem,
(diagonal)² = (length)² +(width)²       {all angles of rectangle are 90°}
          = 15² + 8²
          = 225 + 64  = 289
diagonal   = √289 = √ 17 * 17
          = 17 feet