How long does it take for a sound to travel 126 km by air? On rails?

Path traveled by sound:
S = V * t, where S is the distance (S = 126 km = 126 * 10 ^ 3 m), V is the speed of sound propagation, t is the time of movement.
Sound travel time through the air:
S = V1 * t, where V1 is the speed of sound propagation in air (V = 331 m / s).
t = S / V1 = (126 * 10 ^ 3) / 331 ≈ 381 s.
Sound travel time on rails (steel):
S = V1 * t, where V1 is the speed of sound propagation in steel (V = 6000 m / s).
t = S / V1 = (126 * 10 ^ 3) / 6000 = 21 s.
Answer: Sound will travel the distance in 381 s in the air and in 21 s on the rails.