In order to clean up the construction waste in the school, it takes 12 days for the cooperation of two engineering teams, A and B; A works alone in 1 day, and B works alone in 3 days (3/20). Finally, the school decides to contract the project to Team B. How many days does it take to complete?
为了清扫学校建筑垃圾，甲乙两个工程队合作需耍12天完成；甲独做1天，乙独做3天完成(3/20)，最后学校决定将该项工程承包给乙队独做，请问需要多少天完成？
<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

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

<gadget id="calculator">(3/20) - (1/12)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) / 2</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>