There are 756 books in total, and there are 3 bookshelves, each with 6 floors. On average, how many books are placed on each shelf per shelf?
共有756本书，有3个书架，每个书架有6层．平均每个书架每层放几本书？
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">756 / 18</gadget>
<output>42</output>

<result>42</result>