If three water pipes A, B, and C are used to fill an empty pool at the same time, it can be filled in 1 hour; if two water pipes A and B are used, it can be filled in 1 hour and 20 minutes; if two water pipes B and C are used, 1 hour It can be filled in an hour and 15 minutes, so how many hours will it take to fill this pool of water if you use pipe B to fill it alone?
如果用甲、乙、丙三根水管同时往一个空水池里灌水，1小时可以灌满；如果用甲、乙两根水管，1小时20分可以灌满；如果用乙、丙两根水管，1小时15分可以灌满，那么用乙管单独灌水的话，灌满这一池水需要几小时多少
<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">1 / (4/3)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1 / (5/4)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) - 1</gadget>
<output>-1/5 = around -0.2</output>

<gadget id="calculator">(3/4) + (-1/5)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">1 / (11/20)</gadget>
<output>20/11 = around 1.818182</output>

<result>20/11 = around 1.818182</result>