9. A water pool has three inlet pipes and one outlet pipe. When the outlet and any two of the inlet pipes are opened simultaneously, it takes 6 hours, 5 hours, and 4 hours respectively to fill the entire pool; when the outlet and all three inlet pipes are opened simultaneously, it takes 3 hours to fill the entire pool. If all three inlet pipes are opened simultaneously without the outlet, how many hours will it take to fill the entire pool? $\qquad$
Analysis: In and Out Watering Problem.
Let the full pool water volume be "1",
According to the problem, three inlet efficiencies $\times 2$ - outlet efficiency $\times 3 = \frac{1}{6} + \frac{1}{5} + \frac{1}{4}$
Three inlet efficiencies - outlet efficiency $= \frac{1}{3}$

So the outlet efficiency is $\frac{1}{3} \times 2 - \left(\frac{1}{6} + \frac{1}{5} + \frac{1}{4}\right) = \frac{1}{20}$, the sum of the three inlet efficiencies is $\frac{1}{3} + \frac{1}{20} = \frac{23}{60}$, if only the three inlets are opened, it will take $1 \div \frac{23}{60} = 2 \frac{14}{23}$ hours to fill the entire pool.