Read a book with a smile. On the first day, I read 2/7 of the book. On the second day, I read 10 pages more than the first day. In the end, there are 20 pages left. How many pages are there in this book?
笑笑读一本书，第一天读了这本书的七分之二，第二天比第一天多读了10页，结果还剩20页没读，这本书一共有多少页？
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(2/7) * 2</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 - (4/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">30 / (3/7)</gadget>
<output>70</output>

<result>70</result>