A certain pipe produces a fundamental frequency f in air. If the pipe is filled with helium at the same temperature, what fundamental frequency does it produce? (Take the molar mass of air to be M_air, and the molar mass of helium to be M_He). The ratio γ of heat capacities for air (7/5) and for Helium (5/3). I'm not sure how to approach this question. Any help would be great. Thanks.