For this type of questions (linear equations optimization) remember that the maxumum and minimum values are reached for one of the vertices of the polygon formed by the region.
Now we evaluate the vertices in the given function:
![\begin{gathered} 0+5(2)=10 \\ 6+5(4)=26 \\ 1+5(-1)=-4 \\ 4+5(-1)=-1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/r5atytq5yro7y2pgxndkqd1faw8x8uh335.png)
Then, we conclude that the maximum value is C=26 and the minimum is C=-4.