Question

in order to hear echo, the minium distance between the source and the reflection surface should be​

Answer 1

Answer:

Thus, to hear the echo clearly in the air, the reflecting surface should be at a minimum distance of 16.5m from the source of sound.

Answer 2

Answer:

To hear a clear echo in the air the reflecting surface should be at minimum distance of 16.5m from the source of the sound.