Refer to Solved Problem 1. Start with 20 permanent workers. Prepare a minimum cost plan that may use some combination of hiring ($250 per worker), subcontracting ($8 per unit, maximum of 20 units per month, must use for at least three consecutive months), and overtime ($9 per unit, maximum of 25 units per month). The ending inventory in month 9 should be zero with no back orders at the end. Compute the total cost.