Teacher Li had to correct the homework. He corrected 18 books on the first and second days respectively, and corrected 40 books in total on the third and fourth days. How many books are corrected per day on average?
李老师要批改作业，第一天和第二天各批改了18本，第三天和第四天共批改了40本．平均每天批改了多少本？
<gadget id="calculator">18 + 18 + 40</gadget>
<output>76</output>

<gadget id="calculator">76 / 4</gadget>
<output>19</output>

<result>19</result>