Let x be the number of books to be sold.
The equation can be written as,
[tex]\begin{gathered} 57000+2.5x=16x \\ 57000=16x-2.5x \\ 57000=13.5x \\ \frac{57000}{13.5}=x \\ 4222=x \end{gathered}[/tex]So, the number of books to be sold to break even is 4222.