group of workers are working on a certain project, which was originally planned to be completed in 4 days. If you add 6 people, it only takes 3 days to complete. Now the number of people has not increased, but has decreased by 9 people. Find the number of days needed to complete this project.
有一批工人做某项工程，原计划4天完成．如果增加6人，只需要3天就能完成．现在人数不仅没有增加，反而减少了9人，求完成这项工程需要的天数．
<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

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

<gadget id="calculator">18 - 9</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">18 * (4/9)</gadget>
<output>8</output>

<result>8</result>