It takes 12 days to build a road of 300 meters per day. If an additional 100 meters is built every day, how many days can it be completed? (Solution by proportional method)
修一条公路，每天修300米12天修完，如果每天多修100米，几天可以修完？(用比例方法解)
<gadget id="calculator">300 * 12</gadget>
<output>3_600</output>

<gadget id="calculator">300 + 100</gadget>
<output>400</output>

<gadget id="calculator">3_600 / 400</gadget>
<output>9</output>

<result>9</result>