A man strikes one end of a thin rod with a hammer. The speed of sound in the rod is 16 times the speed of sound in air. A woman, at the other end with her ear close to the rod, hears the sound of the blow twice with a 0.15 s interval between; one sound comes through the rod and the other comes through the air alongside the rod. If the speed of sound in air is 345 m/s, what is the length of the rod?