2. Two pipes can fill a racing pool, emptied at the start, in \( 2 \frac{6}{7} \) hours with the drain kept opened. If the drain were closed at the start the pool would be full in a matter of \( 2 \frac{2}{9} \) hours by the two pipes. If the pipe which can deliver slower, alone did the filling while at the same the drain was opened at the start, it would take the lone pipe 10 hours to do the job. How many hours would it take the drain to empty the pool when full?