Qunli Experimental Primary School has a total of 672 books in three years. There are 3 bookshelves, and each bookshelf has 4 layers. On average, how many books are placed on each layer of each bookshelf?
群力实验小学三年共有672本书．有3个书架，每个书架有4层，平均每个书架每层放几本书？
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">672 / 12</gadget>
<output>56</output>

<result>56</result>