The school library bought 600 new books. Each bookshelf has 3 floors, and each floor has about 20 books. How many more books like this are appropriate?
学校图书馆又新买了600本书，每个书架有3层，每层大约有20本书，增加几个这样的书架比较合适？
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">600 / 60</gadget>
<output>10</output>

<result>10</result>