Person stood between two mountains he hear two echo the first after 2 second, and the second after 2 second from the first echo
Calculate the distance between two mountains when velocity of sound in air equal 340m/s

time of the first echo = 2 seconds
time of the second echo = 2+ 2 = 4 seconds
the distance of the man from the first (nearer) mountain = v*t/ 2 = (340 *2)/2 = 340 m
the distance of the man from the second mountain = (340 * 4) /2 = 680 m
The distance between the two mountains = 340 + 680 = 1020 m = 1.020 Km