A boy standing in front of a large wall,
bangs two objects against each other at
an interval of 1.2 s regularly. The echo of
the first bang coincides with the fifth bang.
If the speed of sound in air is 340 m s–1,
the distance between the boy and the wall is ____.
A 408 m
B 1632 m
C 816 m
D 204 m
No solution is provided.