Yang Yang bought 12 pencils for 9.6 yuan and 12 exercise books for 20.4 yuan. How much is an exercise book more expensive than a pencil?
杨洋买了12只铅笔，用了9.6元，买了12本练习本，用了20.4元，一本练习本比一支铅笔贵多少元？
<gadget id="calculator">20.4 - 9.6</gadget>
<output>10.8</output>

<gadget id="calculator">10.8 / 12</gadget>
<output>0.9</output>

<result>0.9</result>