When Xiao Ming reads a book, the ratio of the number of pages he has read to the number of pages he has not read is 4:5. If he reads 8 more pages, he has read half of the book. Find out how many pages this book has.
小明读一本书，已读的页数和未读的页数比是4：5，如果再读8页，就一共读了这本书的一半，求这本书有多少页．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(1/2) - (4/9)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">8 / (1/18)</gadget>
<output>144</output>

<result>144</result>