Xiao Ming is reading a book. On the first day, he reads (1/4) of the whole book, on the second day he reads the rest (2/5), on the third day he reads 215 pages, and there are 172 pages left. How many pages does this book have?
小明在读一本书，第一天读了整本书的(1/4)，第二天读了剩下部分的(2/5)，第三天读了215页，结果还剩172页．这本书共有多少页？
<gadget id="calculator">215 + 172</gadget>
<output>387</output>

<gadget id="calculator">1 / 4</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">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/4) * (2/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/4) - (3/10)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">387 / (9/20)</gadget>
<output>860</output>

<result>860</result>