The school bought back some exercise books and distributed them to 20 classes, each class had 608 books, and there were 340 books left. How many exercise books did the school buy back?
学校买回一些练习本，发给20个班，每个班608本，还剩340本，学校买回多少本练习本？
<gadget id="calculator">608 * 20</gadget>
<output>12_160</output>

<gadget id="calculator">12_160 + 340</gadget>
<output>12_500</output>

<result>12_500</result>