For a book, Ma Kun read (1/4) of it on the first day and (1/5) of the whole book on the second day. Read 6 pages less on the second day than on the first day. How many pages does this book have?
一本书，马坤第一天看了它的(1/4)，第二天看了全书的(1/5)．第二天比第一天少看6页．这本书共有多少页？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">6 / (1/20)</gadget>
<output>120</output>

<result>120</result>