A manuscript has a total of 400 pages. After typing for 18 days, there are still 40 pages left. How many pages are typed per day on average? (column equation solution)
一本书稿共400页，打字员打了18天后，还剩40页，平均每天打多少页？(列方程解答)
<gadget id="calculator">400 - 40</gadget>
<output>360</output>

<gadget id="calculator">360 / 18</gadget>
<output>20</output>

<result>20</result>