A stone falls into a mine 180 m deep. How many seconds will you hear the sound of a stone

A stone falls into a mine 180 m deep. How many seconds will you hear the sound of a stone on the bottom of the mine? Sound speed in air 330m / s

h = 180 m.
g = 9.8 m / s2.
Vsv = 330 m / s.
t -?
The time t after which the sound of a stone falling on the bottom of the mine will be heard from the moment of its fall will be the sum of t = tp + tsv, where ts is the free fall time of the stone, tsv is the time the sound travels from the bottom of the mine to the observer.
The stone falls from a state of rest with the acceleration of gravity g, therefore the depth of the fall of the stone can be expressed by the formula: h = g * tп2 / 2.
tп = √ (2 * h / g).
tp = √ (2 * 180 m / 9.8 m / s2) = 6 s.
The time of sound movement tsv from the bottom of the mine is expressed by the formula: tsv = h / Vsv.
tsv = 180 m / 330 m / s = 0.6 s.
t = 6 s + 0.6 s = 6.6 s.
Answer: the observer will hear the sound from the beginning of the fall of the stone after t = 6.6 s.