Xiaoli reads a book and reads 90 pages in 3 days. According to this calculation, she just finished reading in a week. How many pages does the book have.
小丽看一本书，3天看了90页，照这样计算，一个星期刚好看完，这本书有多少页．
<gadget id="calculator">90 / 3</gadget>
<output>30</output>

<gadget id="calculator">30 * 7</gadget>
<output>210</output>

<result>210</result>