project can be completed in 6 days by the cooperation of teams A, B and C, and 9 days by the cooperation of teams A and B. How many days can team C do it alone?
一件工程，甲、乙、丙三队合做6天完成，甲、乙两队合做要9天完成．如果丙队独做多少天可以完成？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/6) - (1/9)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / (1/18)</gadget>
<output>18</output>

<result>18</result>