Xiao Ming reads a storybook, 15 pages a day, and finishes it in 12 days. If you read 20 pages a day, how many days can you finish it? (proportional solution)
小明读一本故事书，每天读15页，12天读完．如果每天读20页，几天可以读完？(比例解)
<gadget id="calculator">15 * 12</gadget>
<output>180</output>

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

<result>9</result>