Xiao Ming reads an 840-page story book, and he read a total of 120 pages in the first 3 days. According to this calculation, how many days will it take to finish reading the remaining pages?
小明读一本840页的故事书，前3天共读了120页，照这样计算，剩下的页数还要多少天读完？
<gadget id="calculator">840 - 120</gadget>
<output>720</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">720 / 40</gadget>
<output>18</output>

<result>18</result>