5. (Sec 4.2 Linear Programming: Graphical Methods) Find the maximum and minimum values (if they exist) of the objective function \( f=12 x+ \) \( 8 y \) subject to the following constraints
\[
\left\{\begin{array}{l}
x+2 y \leq 10, \\
2 x+y \leq 11, \\
x+y \leq 9, \\
x \geq 0, y \geq 0
\end{array}\right.
\]
by graphical method.
