Mr. Wang has 48 compositions to correct, and 12 have already been corrected. The rest of the composition should be corrected within 4 hours. How many papers are corrected per hour on average?
王老师要批改48篇作文，已经批改了12篇．剩下的作文要在4小时内改完．平均每小时要批改多少篇？
<gadget id="calculator">48 - 12</gadget>
<output>36</output>

<gadget id="calculator">36 / 4</gadget>
<output>9</output>

<result>9</result>