see here
it is a very similar problem, do you understand it?
A stone is dropped into a deep, dark mine. A clunk is heard 7 seconds later. Estimate the depth of the shaft in feet. Ignore air resistance. Take the speed of sound as 1000 feet/second.
Velocity of sound= 1000 ft/sec
d = 16t^2
can anyone help me to solve this question?
Thank you.