Zhang Yu reads a book. He reads 25% of the book on the first day, and 30% of the book on the second day. There are 36 pages left. How many pages are there in this book?
张宇看一本书，第一天看了这本书的25%，第二天看了这本书的30%，还剩下36页没看，这本书共有多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (3/10) - (1/4)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">36 / (9/20)</gadget>
<output>80</output>

<result>80</result>