There are 9 water pipes in a cistern, one of which is the inlet pipe, and the other 8 are the same outlet pipes. The inlet pipe continuously fills this reservoir with water at a uniform rate. Later, someone wanted to open the outlet pipe to drain all the water in the pool (at this time, some water had been injected into the pool). If all 8 outlet pipes are opened, it will take 3 hours to drain all the water in the pool; if only 5 outlet pipes are opened, it will take 6 hours to drain all the water in the pool. Q: To drain all the water in the pool within 4.5 hours, how many outlet pipes need to be opened at the same time?
有一个蓄水池装有9根水管，其中一根为进水管，其余8根为相同的出水管．进水管以均匀的速度不停地向这个蓄水池注水．后来有人想打开出水管，使池内的水全部排光(这时池内已注入了一些水)．如果把8根出水管全部打开，需3小时把池内的水全部排光；如果仅打开5根出水管，需6小时把池内的水全部排光．问要想在4.5小时内把池内的水全部排光，需同时打开几个出水管？
<gadget id="calculator">5 * 6</gadget>
<output>30</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">30 - 24 - 3</gadget>
<output>3</output>

<gadget id="calculator">4.5 - 3</gadget>
<output>1.5</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">1.5 * 2</gadget>
<output>3</output>

<gadget id="calculator">24 + 3</gadget>
<output>27</output>

<gadget id="calculator">27 / 4.5</gadget>
<output>6</output>

<result>6</result>