Plan D$$:

Keep the current workforce stable at producing $1$ comma $600$

units per month. In addition to the regular$$ production, another $20$

$\%$

of the normal production units can be produced in overtime at an additional cost of $$$$50$

per unit. A warehouse now constrains the maximum allowable inventory on hand to $400$

units or less. If production$$ and$/$or inventory are$$ adequate, do not produce any units in overtime.