The cement factory produces a batch of cement. It originally planned to complete 15 tons per day, but the task can be completed on time; the actual production is 18 tons per day, but the task was completed in 25 days. How many days did it take to complete the task as originally planned? (Solution with proportional knowledge)
水泥厂生产一批水泥，原计划每天完成15吨，可以按时完成任务；实际每天生产18吨，结果25天就完成了任务，原计划完成任务要多少天？(用比例知识解)
<gadget id="calculator">18 * 25</gadget>
<output>450</output>

<gadget id="calculator">450 / 15</gadget>
<output>30</output>

<result>30</result>