If a pipe's center line is 9 feet above the finished floor and there is a benchmark that is 2 feet above the finished floor, what is the pipe's center line elevation relative to the benchmark?

To determine the pipe's center line elevation relative to the benchmark, we need to calculate the difference between the elevation of the pipe and the elevation of the benchmark.

The pipe's center line is 9 feet above the finished floor, while the benchmark is at an elevation of 2 feet above the finished floor. To find the relative elevation of the pipe compared to the benchmark, we subtract the benchmark elevation from the pipe's elevation:

9 feet (pipe center line) - 2 feet (benchmark) = 7 feet.

Therefore, the pipe's center line elevation relative to the benchmark is 7 feet. Since this matches one of the answer choices, option C is the correct answer.

6 feet is not the correct option because it does not represent the difference calculated from the two elevations. Similarly, 5 feet, while a potential miscalculation that could arise from incorrect subtraction, does not reflect the actual relationship between the pipe's elevation and the benchmark. Finally, 8 feet exceeds the actual difference, showing a misunderstanding of the calculation regarding the two elevations.