Xiao Ming reads a storybook, and plans to read 15 pages a day, and it takes 12 days to finish reading. If you read 20 pages a day, how many days can you finish reading in advance?
小明读一本故事书，计划每天读15页，需12天读完．如果每天读20页，则可以提前多少天读完．
<gadget id="calculator">15 / 20</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">12 * (3/4)</gadget>
<output>9</output>

<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<result>3</result>