It Costs $20 to Make a Single Unit Using Regular

It costs $20 to make a single unit using regular production and $25 to make a single unit using overtime production. Total overtime production is limited to 50 units for the five-month period. The manufacturing plant has a regular production capacity of 300 units per month and no units in inventory at the start of the planning period. There is a $10 per unit charge for holding inventory at the end of each month and the ending inventory of the five-month planning period should be zero. Develop an objective function and constraints to solve this problem.
$$\begin{array} { | l | c | } \hline { \text { Month } } & \text { Forecast } \\\hline \text { August } & 250 \\\hline \text { September } & 200 \\\hline \text { October } & 300 \\\hline \text { November } & 400 \\\hline \text { December } & 500 \\\hline\end{array}$$