A and B work together to complete a job in 5 hours, and B and C work together in 4 hours. If B works alone for 6 hours, A and B work together for 2 hours to complete the task. How many hours does it take B to finish it alone?
一件工作，甲、乙合做5小时完成，乙、丙合做4小时完成，如果乙单独做6小时后，甲、乙再合做2小时，也刚好完成任务．乙单独做完需要几小时？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 2</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) / 6</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / (1/10)</gadget>
<output>10</output>

<result>10</result>