If three water pipes A, B, and C are used to fill an empty pool at the same time, it can be filled in one hour; if two pipes A and B are used, it can be filled in one hour and 20 minutes; if two water pipes B and C are used, It can be filled in 1 hour and 15 minutes, so how many hours will it take to fill the pool with water by pipe B alone?
如果用甲、乙、丙三那根水管同时在一个空水池里灌水，1小时可以灌满；如果用甲、乙两管，1小时20分钟可以灌满；如果用乙、丙两根水管，1小时15分钟可以灌满，那么，用乙管单独灌水的话，灌满这一池的水需要多少小时？
<gadget id="calculator">1_200 / 80</gadget>
<output>15</output>

<gadget id="calculator">1_200 / 75</gadget>
<output>16</output>

<gadget id="calculator">1_200 / 60</gadget>
<output>20</output>

<gadget id="calculator">16 - 20</gadget>
<output>-4</output>

<gadget id="calculator">15 + (-4)</gadget>
<output>11</output>

<gadget id="calculator">1_200 / 11</gadget>
<output>1_200/11 = around 109.090909</output>

<result>1_200/11 = around 109.090909</result>