An old mining tunnel disappears into a hillside. You would like to know how long the tunnel is, but it's too dangerous to go inside. Recalling your recent physics class, you decide to try setting up standing-wave resonances inside the tunnel. Using your subsonic amplifier and loudspeaker, you find resonances at 5.0 Hz and 7.0 Hz , and at no frequencies between these. It's rather chilly inside the tunnel, so you estimate the sound speed to be 340 m/s . Based on your measurements, how far is it to the end of the tunnel