A pool can be filled with water from three pipes A, B, and C. It takes 10 hours to fill up pipe A alone, 12 hours to fill pipe B alone, and 15 hours to fill pipe C alone. Now after pipes A, B, and C are opened for 1 hour, the remaining pipes are required to be filled within 3 and a half hours, and pipe C is used as little as possible, so how many hours did pipe C spend in this water injection?
某水池可用A、B、C三个水管注水，单开A管注满要10小时，单开B管注满要12小时，单开C管注满要15小时．现在A、B、C管合开1小时后，要求余下的在3小时半内注满，且尽量少用C管，则C管在这次注水中共注了多少小时．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/10) + (1/12)</gadget>
<output>11/60 = around 0.183333</output>

<gadget id="calculator">1 + 3.5</gadget>
<output>4.5</output>

<gadget id="calculator">(11/60) * 4.5</gadget>
<output>0.825</output>

<gadget id="calculator">1 - 0.825</gadget>
<output>0.175</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">0.175 / (1/15)</gadget>
<output>2.625</output>

<result>2.625</result>