It takes 10 hours for two different tractors A and B to plow a piece of land together. After working together for 4 hours, tractor A breaks down, and tractor B has to plow another 18 hours alone. If tractor A plows the field alone, how many hours can the task be completed.
甲、乙两台不同的拖拉机合耕一块地共需10小时，在共同工作4小时后，甲拖拉机发生故障，由乙拖拉机单独又耕了18小时才完成．如果由甲拖拉机单独耕这块地，多少小时可以完成任务．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) / 18</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/10) - (1/30)</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>