In the library, Mr. Li distributed some extracurricular reading materials to 12 classes on average, and each class got 42 books, leaving 35 books left. How many books are there in total?
图书室李老师将一些课外读物，平均分给12个班，每班分到42本，还剩下35本．这些课外读物一共有多少本？
<gadget id="calculator">12 * 42</gadget>
<output>504</output>

<gadget id="calculator">504 + 35</gadget>
<output>539</output>

<result>539</result>