A project, which is constructed by engineering team A alone, takes 6 days to complete. Construction by engineering team B alone will take 12 days to complete. How many days will it take for the two teams to work together?
一项工程，由甲工程队单独施工，需6天完成．由乙工程队单独施工，需12天完成．两队共同施工，需多少天完成．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

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

<gadget id="calculator">(1/6) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

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

<result>4</result>