For an empty pool, if the inlet pipes A and B are opened separately, it will take 18 hours and 15 hours to fill up, respectively, and it will take 12 hours to empty the pool with the drain pipe C alone. Now pipes A, B, and C are turned on alternately for one hour each until the empty pool is filled. How many hours will it take in total?
一个空水池，如果单独开进水管A，B，注满分别需要18小时和15小时，单独开排水管C排空一池水需12小时．现在A，B，C三管轮流交替各开一小时，直到将空池注满．一共需要多少小时？
<gadget id="calculator">25 * 3</gadget>
<output>75</output>

<gadget id="calculator">7 / 180</gadget>
<output>7/180 = around 0.038889</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(5/7) / (1/18)</gadget>
<output>90/7 = around 12.857143</output>

<gadget id="calculator">(7/180) * (90/7)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">75 + (1/2)</gadget>
<output>151/2 = around 75.5</output>

<result>151/2 = around 75.5</result>