Xiaowen reads a book. He reads (1/4) of the whole book in the first week, and (1/5) of the whole book in the second week. There are 165 pages left. How many pages does this book have?
小文看一本书，第一周看了全书的(1/4)，第二周看了全书的(1/5)，还剩165页没有看，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 - (1/4) - (1/5)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">165 / (11/20)</gadget>
<output>300</output>

<result>300</result>