Students from 4 classes in the third grade donated books. Class 1 and Class 2 donated 23 books, Class 3 donated 15 books, Class 4 donated 22 books, and the average number of books donated by each class.
三年级4个班同学捐图书，一班和二班共捐23本，三班捐了15本，四班捐了22本，平均每班捐图书多少本．
<gadget id="calculator">23 + 15 + 22</gadget>
<output>60</output>

<gadget id="calculator">60 / 4</gadget>
<output>15</output>

<result>15</result>