For a book, Xiaohong read 25% of the book on the first day, 15 pages on the second day, and left 75 pages unread. How many pages does this book have?
一本书，小红第一天看了全书的25%，第二天看了15页，还剩75页没有看，这本书共有多少页？
<gadget id="calculator">15 + 75</gadget>
<output>90</output>

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

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">90 / (3/4)</gadget>
<output>120</output>

<result>120</result>