Wang Ming reads a book. After reading several pages, the ratio of the number of pages read to the number of unread pages is 2:3. If he reads 5 more pages, the ratio of the number of pages read to the number of unread pages is 2:3. The ratio of pages is 9:11. How many pages does this book have?
王明读一本书，读了若干页后，这时已读的页数和未读的页数的比是2：3，如果再读5页，这时已读的页数和未读的页数的比是9：11．这本书有多少页？
<gadget id="calculator">9 + 11</gadget>
<output>20</output>

<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(9/20) - (2/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">5 / (1/20)</gadget>
<output>100</output>

<result>100</result>