I read an extra-curricular book on weekends. I read (1/4) of the whole book on the first day and 15 pages on the second day. At this time, the ratio of the number of pages I have read to the number of pages I have not read is 2:3. How many pages does the book have?
双休日明明看一本课外书，第一天看了全书的(1/4)，第二天看了15页，这时已看的页数与未看页数的比是2：3，这本书共有多少页？
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

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

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

<gadget id="calculator">(2/5) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">15 / (3/20)</gadget>
<output>100</output>

<result>100</result>