The school bought 640 books, which are going to be placed on 2 bookshelves. Each bookshelf has 4 layers. How many books are placed on each layer?
学校买来640本书，准备放在2个书架上，每个书架有4层，平均每层放几本？
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">640 / 8</gadget>
<output>80</output>

<result>80</result>