12. Xiaoli and Xiaoying both have some comic books. If Xiaoying gives Xiaoli 7 comic books, Xiaoli's number of comic books will be 5 times that of Xiaoying. If Xiaoli gives Xiaoying 9 comic books, Xiaoli's number will be 3 times that of Xiaoying. Originally, Xiaoying had ( ) comic books, and Xiaoli had ( ) comic books.
【Analysis】Let Xiao Ying have $x$ books, and Xiao Li have $y$ books
$$
\left\{\begin{array} { l } 
{ 5 ( x - 7 ) = y + 7 } \\
{ 3 ( x + 9 ) = y - 9 }
\end{array} \Rightarrow \left\{\begin{array}{l}
x=39 \\
y=153
\end{array}\right.\right.
$$