Xiaohong finished a book in 3 days. She read 30% of the book on the first day, read the whole book (9/20) on the second day, and read 120 pages on the third day. How many pages does this book have?
晓红3天看完一本书，第一天看了全书的30%，第二天看了全书的(9/20)，第三天看了120页，这本书一共有多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

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

<gadget id="calculator">(3/10) + (9/20)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">120 / (1/4)</gadget>
<output>480</output>

<result>480</result>