Uncle Wang has to transport 240 pages of the book and has already read 180 pages. If he reads 15 pages an hour, how many hours will it take to finish reading?
王叔叔要运240页书，已经已经读了180页，如果每小时读15页，还要几小时才能读完？
<gadget id="calculator">240 - 180</gadget>
<output>60</output>

<gadget id="calculator">60 / 15</gadget>
<output>4</output>

<result>4</result>