A road construction team plans to build a road with a length of 840m. In the first 15 days, a total of 420m was built. Based on this calculation, how many days will it take to complete the road?
一个修路队计划修一条长840m的公路，前15天一共修了420m，照这样计算，修完这条公路还需要多少天？
<gadget id="calculator">840 - 420</gadget>
<output>420</output>

<gadget id="calculator">420 / 15</gadget>
<output>28</output>

<gadget id="calculator">420 / 28</gadget>
<output>15</output>

<result>15</result>