Xiaofang reads a book. She reads 40% of the whole book on the first day, and 45% of the whole book on the second day. She reads 15 more pages on the second day than on the first day. How many pages does this book have?
小芳看一本书，第一天看了全书的40%，第二天看了全书的45%，第二天比第一天多看了15页，这本书有多少页？
<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">40 / 100</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">15 / (1/20)</gadget>
<output>300</output>

<result>300</result>