15. Given $A(-2,4) 、 B(3,-1) 、 C(-3,-4)$, and $\overrightarrow{C M}=3 \overrightarrow{C A}, \overrightarrow{C N}=$ $2 \overrightarrow{C B}$, find the coordinates of $M 、 N$ and $\overrightarrow{M N}$.
15. Let $M(x, y), \overrightarrow{C M}=\{x+3, y+4\}, \overrightarrow{C A}=\{1,8\}$. From $\overrightarrow{C M}=3 \overrightarrow{C A}$ we get $\left\{\begin{array}{l}x+3=3 \\ y+4=24,\end{array}\right.$ which means $\left\{\begin{array}{l}x=0 \\ y=20,\end{array}\right.$ so $M(0,20)$. Similarly, $N(9,2), \overrightarrow{M N}=\{9,-18\}$.