cleetus wrote:
I got the answer here right. But still am not 100% clear how the speed of sound determines the distance he traveled and how the 30 seconds difference helps here
Let us first assume that the person is not moving and standing still. In that case he would have heard the 2nd blast exactly after 30 min.
Now as the person has moved some distance after the first blast (according to the question) the sound has to travel that extra distance to reach the person. So the delay in the time between the actual blast and the time when he heard is the time taken by sound to travel and reach him.
which is 30 sec* speed of sound = 9900 m