A can do a job alone in 20 hours, B can do it in 30 hours, and C can do it in 40 hours. Now the three are working together, and A paused for a few hours because of other things. As a result, it took 12 hours to complete from the beginning. How many hours did A pause in the middle?
一件工作，甲单独做要20小时，乙单独做要30小时完成，丙单独做要40小时完成．现在三人合作，甲因其它事中间暂停了几小时，结果从开始算起，用了12小时完成．问甲中间暂停了几小时？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/30) + (1/40)</gadget>
<output>7/120 = around 0.058333</output>

<gadget id="calculator">(7/120) * 12</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(3/10) / (1/20)</gadget>
<output>6</output>

<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<result>6</result>