A project is planned to be done by 30 people, and it can be completed in 15 days. Due to work needs, 5 people left for investigation. How many days can actually complete the project?
一项工程，计划由30人做，15天就可以完成，因工作需要调查走了5人，实际多少天能完成这项工程？
<gadget id="calculator">30 * 1 * 15</gadget>
<output>450</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<gadget id="calculator">450 / 25 / 1</gadget>
<output>18</output>

<result>18</result>