Xiaohong read a 196-page story book, and read 28 pages in the first 3 days. According to this calculation, how many days will it take to finish reading this book?
小红读一本196页的故事书，头3天读了28页．照这样计算，读完这本书还要几天？
<gadget id="calculator">21 - 3</gadget>
<output>18</output>

<result>18</result>