Question 881508
Six hours filling while the drain is open, and then some t hours of filling with the drain shut.


Use positive for FILLING the pool and NEGATIVE or subtraction for DRAINING the pool.


R*T=J, considering filling the pool to be one job.  R is rate, T is time.



Let t be time in hours of filling while the 
drain is shut.
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{{{highlight((1/6-1/9)6+(1/6)t=1)}}}
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If you understand the analysis explained, and the resulting equation, then THAT is most of the problem solution.  Solve for t.