The school bought 680 books and distributed them to students in 12 classes in the fourth grade, and each class distributed 45 books. How many books are left in school?
学校买来680本图书，发给四年级12个班的同学，每个班发了45本．学校还剩多少本图书？
<gadget id="calculator">12 * 45</gadget>
<output>540</output>

<gadget id="calculator">680 - 540</gadget>
<output>140</output>

<result>140</result>