A vessel contains a 20. cm high column of water and a layer of carbon tetrafluoride of unknown thickness (the two layers do not mix). A high-frequency sound wave propagates vertically into the liquids. The ratio N_w/N_T = 0.83 (#cycles in water to #cycles in carbon tetrafluoride). Find the thickness of the carbon tetrafluoride layer. Take the speed of sound in water as 1493 m/s and in carbon tetrafluoride as 930 m/s.