A book has 140 pages, Xiao Ming has already read 20 pages, and he wants to finish the rest within 3 days, how many pages should he read on average.
一本书140页，小明已经看了20页，剩下的他想在3天内看完，平均要看多少页．
<gadget id="calculator">140 - 20</gadget>
<output>120</output>

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

<result>40</result>