I read a book with a smile. I read (1/4) of this book in the first week, and (2/7) of this book in the second week. I read 20 more pages in the second week than in the first week. How many pages does this book have?
笑笑看一本书，第一周看了这本书的(1/4)，第二周看了这本书的(2/7)，第二周比第一周多看了20页，这本书共有多少页？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/7) - (1/4)</gadget>
<output>1/28 = around 0.035714</output>

<gadget id="calculator">20 / (1/28)</gadget>
<output>560</output>

<result>560</result>