The school library bought 3 new bookshelves, each with 5 floors, containing 135 books in total. How many books are placed on each floor on average?
学校图书室新买了3个书架，每个书架5层，一共装书135本．平均每层放多少本书？
<gadget id="calculator">135 / 3 / 5</gadget>
<output>9</output>

<result>9</result>