Mr. Chen has revised 48 speeches, 12 of which have been revised. If the remaining 9 speeches are revised every hour, how many hours will it take to finish?
陈老师修改48篇演讲稿，已修了12篇，剩下的如果每小时修9篇，还需要多少小时才能修完？
<gadget id="calculator">48 - 12</gadget>
<output>36</output>

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

<result>4</result>