A project, if A and B work together, can complete half of the project in 3 days; if C works alone, it can be completed in 12 days. Now A, B, C cooperate, how many days can complete the whole project?
一项工程，如果甲、乙合作3天可以完成这项工程的一半；如果丙单独做，12天可以完成．现在甲、乙、丙合作，几天可以完成全部工程？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 3</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>