Xiaoxue reads a book, reads 40% of the whole book on the first day, and reads 12 pages more than the whole book (1/4) on the second day. At this time, the ratio of the number of pages read to the number of unread pages is 3: 1. How many pages does this book have?
小雪读一本书，第一天读了全书的40%，第二天读的比全书的(1/4)还多12页，这时已读页数和未读页数的比是3：1．这本书共有多少页？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(3/4) - (2/5) - (1/4)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">12 / (1/10)</gadget>
<output>120</output>

<result>120</result>