Xiaoling reads a book. She reads (1/5) of this book on the first day and (1/4) of this book on the second day. She reads 180 pages in total in two days. How many pages are there in this book? Page?
小玲看一本书，第一天看了这本书的(1/5)，第二天看了这本书的(1/4)，两天一共看了180页，这本书有多少页？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) + (1/4)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">180 / (9/20)</gadget>
<output>400</output>

<result>400</result>