A certain project can be completed in 12 days by A alone, and 36 days by B alone. If the two cooperate, how many days will it take to complete it?
某项工程，甲单独做需12天完成，乙单独做则需36天完成如果两合作，则需要多少天可完成．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 36</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>