What we must do is equal both equations like this:
[tex]15756+23.5\cdot x=48108+12\cdot x[/tex]solving for x (numbers of books):
[tex]\begin{gathered} 23.5\cdot x-12\cdot x=48108-15756 \\ 11.5\cdot x=32352 \\ x=\frac{32352}{11.5} \\ x=2813.2=2813 \end{gathered}[/tex]In aproximately 2813 books