The school library bought 600 books and put them on the bookshelves. Each bookshelf has 5 layers, and each layer contains 20 books. How many bookshelves are needed in total?
学校图书馆买来600本书，要放在书架上，每个书架有5层，每层放20本书，一共需要多少个书架？
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">600 / 100</gadget>
<output>6</output>

<result>6</result>