Smiling and reading a technical book, the ratio of the number of pages read on the first day to the total number of pages in the book is 2:7. If you read another 45 pages, you can read the entire book (1/2). How many pages does this book have?
笑笑看一本科技书，第一天看的页数与全书总页数的比是2：7，如果再看45页，就可以看完全书的(1/2)．这本书共有多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(1/2) - (2/7)</gadget>
<output>3/14 = around 0.214286</output>

<gadget id="calculator">45 / (3/14)</gadget>
<output>210</output>

<result>210</result>