Correct Answer - 27
Time interval between beats (initially) `= (60)/(40) = 1.5` sec
Since `t = (2S)/(v)`
`1.5 = (2S)/(2v)`
where `S` is the initial distance and `v` is the speed of sound . As the man approches `90m` towards the mountain
`(2(S - 90))/(v) = 1` , since drumming rate is `60//min`
Solving for `S` from the two relations we get
`(2S)/(2(S - 90)) = 1.5 , (S - 90)/(S) = (2)/(3) rArr 3S - 3 xx 90 = 2S , S = 270 m`