A pool has two inlet taps A and B and one outlet tap C. If both taps A and C are opened when the pool is empty, the pool can be filled in 2 hours; taps B and C can be opened in 3 hours to fill the pool. When the water is full, turn on C first, turn on A and B at the same time after 7 hours (C is still on), and the pool can be filled after 1 hour. Then open A alone, how many hours can the pool be filled?
一水池有A、B两个进水龙头和一个出水龙头C，如果在水池空时同时将A、C打开，2小时可注满水池；同时打开B、C两龙头3小时可注满水池．当水满时，先打开C，7小时后把A、B同时打开(C仍开着)，1小时后水池可注满．那么单独打开A，几小时可注满水池？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) - 1</gadget>
<output>-2/3 = around -0.666667</output>

<gadget id="calculator">1 + (1/2) + (-2/3)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 - 1 - 1</gadget>
<output>-1</output>

<gadget id="calculator">7 + (-1)</gadget>
<output>6</output>

<gadget id="calculator">(5/6) / 6</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">(5/36) + (1/2)</gadget>
<output>23/36 = around 0.638889</output>

<gadget id="calculator">1 / (23/36)</gadget>
<output>36/23 = around 1.565217</output>

<result>36/23 = around 1.565217</result>