If you read 30 pages a day, you can finish reading a book in 6 days. If you read 20 pages a day, how many days will it take to finish reading?
一本书，如果每天读30页，6天可以读完，若每天读20页，要多少天才能读完？
<gadget id="calculator">30 * 6</gadget>
<output>180</output>

<gadget id="calculator">180 / 20</gadget>
<output>9</output>

<result>9</result>