A hunter is standing on flat ground between two vertical cliffs that are directly opposite one another. He is closer to one cliff than to the other. He fires a gun and, after a while, hears three echoes. The second echo arrives 1.9 sec after the first, and the third echo arrives 1 sec after the second. Suppose that the speed of sound is 343 m/s and that there are no reflections of sound from the ground, compute the distance between the cliffs.