A boy stands between two vertical walls and fires a rifle. Under what condition will he hear a single echo from both walls? Calculate the distance between the walls if the single echo is heard six seconds later.​

d = 1,029 m

Explanation:

When the young man shoots the rifle the sound travels in all directions, if the young man is at the same distance from the two walls, as the speed of the wave is constant, he takes the same time to go to the wall and return for which he hears a single echo.

To calculate the distance let's use the uniform motion relationships

        v = d / t

        d = v t

As the speed is constant, the time to reach the wall is the same as it takes to go from the wall to the young man,

         t = to / 2

         t = 6/2

         t = 3 s

         d = 343 3

         d = 1,029 m