Xiao Ming has a book. He read 25% of the book on the first day and 21 pages on the second day. At this time, the ratio of the number of pages he has read to the number of pages he has not read is 3:2. How many pages does this book have?
小明有一本书，第一天看了全书的25%，第二天看了21页，这时已看的和未看的页数的比是3：2．这本书一共有多少页？
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">(3/5) - (1/4)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">21 / (7/20)</gadget>
<output>60</output>

<result>60</result>