A storybook can be finished in 15 days if you read 14 pages a day. If you read 21 pages a day, how many days can you finish reading?
一本故事书，如果每天读14页，15天可以读完．如果每天读21页，多少天可以读完？
<gadget id="calculator">15 * 14</gadget>
<output>210</output>

<gadget id="calculator">210 / 21</gadget>
<output>10</output>

<result>10</result>