Xiao Ming reads a book, and reads part of it in the morning. At this time, the ratio of the number of pages read to the number of unread pages is 1:9; in the afternoon, he reads 6 more pages than in the morning. At this time, the number of pages read and the number of unread pages The ratio becomes 1:3. How many pages is this book?
小明读一本书，上午读了一部分，这时读的页数与未读页数的比是1：9；下午比上午多读6页，这时已读的页数与未读的页数的比变成了1：3．这本书共多少页？
<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">6 / (1/20)</gadget>
<output>120</output>

<result>120</result>