In the first week, Xiaowen had read a quarter of the book, which meant that she had read 1/4 of the book. In the second week, Xiaowen had read one-fifth of the book, which meant that she had read 1/5 of the book. The ratio of the remaining books was $1-1/4-1/5=16/20$. Because Xiaowen hadn't finished reading the entire book, she needed to look at the ratio of $16/20$, which was $8/20$. If the book has a total of $x$pages, then $x=16/20*165$. The solution is $x=2400$. So the book had a total of $2400 pages.