project can be completed by Team A alone in 12 days, and the work efficiency of Team B is 1/3 of that of Team A. If Team A and Team B cooperate to complete this project, how many days can they complete the project.
一项工程，甲队独做要12天完成，乙队的工作效率是甲队的(1/3)，如果甲、乙两队合作共同完成这项工程，多少天可以全部完成这项工程．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/12) * (1/3)</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">(1/12) + (1/36)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / (1/9)</gadget>
<output>9</output>

<result>9</result>