Two rifles are fired from the same place at a difference of 11 minutes 45 seconds. But a man who is coming towards the place in a train hears the second sound after 11 minutes. Find the speed of train. (speed of sound = 330 m/s)

Answer: Option C

Distance travelled by man-train in 11 minute = distance traveled by sound in (11 min 45 sec - 11 min) = 45 sec.
Let the speed of train be x kmph.
Now,
Or, $$x\times \frac{11}{60}=\frac{45}{3600}\times 330\times \frac{18}{5}$$
Or, x = 81 kmph.