problem on beats , pleaseeee helppppp!!! I am puzzled!! problem----- A man standing in front of a mountain beats a drum at regular intervals. The drumming rate is gradually increased and he finds that the echo is not heard distinctly when the rate becomes 40 per minute. He moves nearer to the mountain by 90 meters and finds that the echo is again not heard when drumming rate becomes 60 per minute. Calculate (a) the distance between the mountain and initial position of the man , and (b) the velocity of the sound. I am desperate for helpppppp.