The school spent 864 yuan to buy 8 packs of books, each pack of 9 books, how much is the average per book?
学校用864元买了8包书，每包9本书，平均每本书多少元？
<gadget id="calculator">864 / 8</gadget>
<output>108</output>

<gadget id="calculator">108 / 9</gadget>
<output>12</output>

<result>12</result>