First read 15 pages of a book, and then read (1/3) of the whole book, and (1/4) of the whole book is left. How many pages are there in this book?
一本书先看了15页，又看了全书的(1/3)，还剩下全书的(1/4)，这本有多少页．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/4) - (1/3)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">15 / (5/12)</gadget>
<output>36</output>

<result>36</result>