Solve the Following LP Problem Graphically Using Level Curves

Short Answer

Solve the following LP problem graphically using level curves.
$$\begin{array} { l l } \text { MAX: } & 7 X _ { 1 } + 4 X _ { 2 } \\\text { Subject to: } & 2 X _ { 1 } + X _ { 2 } \leq 16 \\& X _ { 1 } + X _ { 2 } \leq 10 \\& 2 X _ { 1 } + 5 X _ { 2 } \leq 40 \\& X _ { 1 } X _ { 2 } \geq 0\end{array}$$