To build a 400m road, 120m was built in the first 3 days. At this speed, how many days will it take to complete the road.
修一条400m的公路，前3天修了120m，照这样的速度，修完这条公路共需要多少天．
<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">400 / 40</gadget>
<output>10</output>

<result>10</result>