t = total time taken by sound to go down the well and then come back = 2 sec
d = depth of the well
D = total distance traveled by the sound
total distance traveled by sound is given as
total distance traveled = distance traveled going down + distance traveled going up
D = d + d
D = 2 d eq-1
v = speed of sound = 343 m/s
we know that distance traveled is given as
total distance traveled = speed of sound x total time
D = v t
using eq-1
2 d = v t
2 d = (343) (2)
dividing both side by 2
d = 343 x 2/2
d = 343 m
hence surface of water is 343 m deep