There is a well. In the absence of water seepage, pump A can pump all the water in 20 hours, and pump B can pump all the water in 12 hours. Now two pumps A and B are pumping water at the same time. Due to water seepage, it takes 9 hours to pump the water completely. In the case of water seepage, how many hours does it take to use a water pump alone to pump it out?
有一口水井．在无渗水的情况下，甲抽水机用20小时可将水抽完，乙抽水机用12小时可将水抽完．现在甲、乙两台抽水机同时抽，由于有渗水，结果用9小时才将水抽完．在有渗水的情况下，用甲抽水机单独抽需多少小时抽完？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(1/20) + (1/12)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">(2/15) * 9</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(6/5) - 1</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 9</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/20) - (1/45)</gadget>
<output>1/36 = around 0.027778</output>

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

<result>36</result>