vb6-4) Two sound pipes, the first open on both sides, the second closed on one side, are blown with air at 20 ° C,  so that the open pipe produces its fundamental tone and the closed pipe produces its first overtone.  The latter is the highest and gives 10 beats per second with the former. 
The closed pipe is then filled with a two-atom ideal gas with a relative density of 0.16. 
The root note of both tubes is now equally high. 

Determine the length of each tube.