a gun is fired by a person is standing in a large open field between two high mountains 150 m from the nearest mountain; so that he hears marked echoes, separated by a time interval 1 sec caculate the distance between the two mountains assuming that the speed of soun in air is 340 m/s

The time for the echo to come back from the nearer mountain is

t = 2d/v = 300/340 = .88 sec

So, the time for the later echo is 1.88 sec

d = vt/2 = 340 * 1.88 = 319.6m