4 hard cover books are 48 yuan, 3 soft cover books are 63 yuan, which book is more expensive? How much is it expensive?
4本硬皮本48元，3本软皮本63元，哪种本子贵一些？贵多少元？
<gadget id="calculator">63 / 3</gadget>
<output>21</output>

<gadget id="calculator">48 / 4</gadget>
<output>12</output>

<gadget id="calculator">21 - 12</gadget>
<output>9</output>

<result>9</result>