Zhongliu Village needs to build a 504-meter-long canal. It is known that 84 meters were built in the first three days. How many days will it take to finish the rest?
中刘村要修一条504米长的水渠，已知前三天修了84米，剩下的还要多少天修完？
<gadget id="calculator">504 - 84</gadget>
<output>420</output>

<gadget id="calculator">84 / 3</gadget>
<output>28</output>

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

<result>15</result>