The school repaired 2640 books, and 240 books were repaired in the first 3 hours. According to this calculation, how many hours will it take to repair the rest?
学校修补图书2640本，前3个小时修补了240本，照这样计算，余下的还要几个小时修补完？
<gadget id="calculator">2_640 - 240</gadget>
<output>2_400</output>

<gadget id="calculator">240 / 3</gadget>
<output>80</output>

<gadget id="calculator">2_400 / 80</gadget>
<output>30</output>

<result>30</result>