When Li Hong reads a book, he reads part of it on the first day, accounting for 1/9 of the unread, and reads 7 more pages on the second day than on the first day. At this time, the ratio of the number of pages read to the number of unread pages is 1:3, how many pages does this book have?
李红读一本书，第一天读了一部分，占未读的(1/9)，第二天比第一天多读7页，这时已读页数与未读页数的比是1：3，这本书一共多少页？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">1 + 9</gadget>
<output>10</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">7 / (1/20)</gadget>
<output>140</output>

<result>140</result>