Dig a canal 1,800 meters long and complete 840 meters in 7 days. At this speed, how many days will it take to complete the project? (Answer with proportional knowledge)
挖一条水渠长1800米，7天完成840米，照这样速度，完成这项工程要多少天？(用比例知识解答)
<gadget id="calculator">840 / 7</gadget>
<output>120</output>

<gadget id="calculator">1_800 / 120</gadget>
<output>15</output>

<result>15</result>