If A alone can complete a project in 30 days, and teams A and B can complete it in 12 days, how many days will it take for B to complete the project alone?
一项工程甲单独做30天完成，甲、乙两队合做12天完成，那么乙单独做完成这项工程要多少天．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/12) - (1/30)</gadget>
<output>1/20 = around 0.05</output>

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

<result>20</result>