Xiao Ming reads a book and reads part of it on the first day. The ratio of pages read to unread is 2:7. He reads 68 pages on the second day, and the ratio of pages read to unread is 4:5. ． How many pages does this book have?
小明看一本书，第一天读了一部分，已读的和未读的页数比是2：7，第二天读了68页，已读的和未读的页数比是4：5．这本书共有多少页？
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

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

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">(4/9) - (2/9)</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">68 / (2/9)</gadget>
<output>306</output>

<result>306</result>