Suppose you can use a combination of overtime and subcontracting, but you cannot use subcontracting in more than two periods, there is 6 periods. Up to 50 units of subcontracting and either 0 and 40 units of overtime are allowed per period. Subcontracting is $6 per unit, and overtime is $3 per unit. (Hint: use subcontracting only when overtime units are not sufficient to decrease backlogs to 80 units or less.) Plan for an ending inventory balance of 0 for period 6. Prepare a plan that will minimize total cost.