Answer:
4√41 ≈ 25.61 feet
Explanation:
The shortest route is the one that crosses the longest edge between room surfaces. In this case, that is the 16-foot edge between the floor and wall opposite the amplifier, or the 16-foot edge between the ceiling and the wall adjacent to the amplifier.
The length of the required wire is ...
√((8+12)² +16²) = √656 = 4√41 ≈ 25.61 . . . feet