Q: 4 (NDA-I/2008)

A man standing between two parallel hills fires a gun and hears two echoes, one
2.5 s and the other
3.5 s after the firing. If the velocity of sound is 330 ms-1, how long will it take him to hear the third echo?
question_subject: 
Science
stats: 
0,104,232,88,128,104,16