It takes 8 hours for A to produce a batch of parts alone. Now after A has been working for 2 hours, B joins the work, and the two cooperate and spend another 4 hours to complete the task. How many hours does it take B to produce this batch of parts alone?
一批零件，甲单独生产要8小时完成．现在甲做了2小时后，乙参加工作，二人合作又用了4小时完成了任务．乙单独生产这批零件要多少小时．
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<gadget id="calculator">(1/8) * 6</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) / 4</gadget>
<output>1/16 = around 0.0625</output>

<gadget id="calculator">1 / (1/16)</gadget>
<output>16</output>

<result>16</result>