To build a road, it is planned to build 3 kilometers per day, and it can be completed in 45 days. The actual repair is 3.6 kilometers per day, and the task is actually completed a few days ahead of schedule.
修一条公路，计划每天修3千米，45天可以修完，实际每天修3.6千米，实际提前几天完成任务．
<gadget id="calculator">45 / 3.6</gadget>
<output>12.5</output>

<gadget id="calculator">3 * 12.5</gadget>
<output>37.5</output>

<gadget id="calculator">45 - 37.5</gadget>
<output>7.5</output>

<result>7.5</result>