Refer to Solved problem 1. Start with 20 permanent workers. Prepare minimum cost aggregate plan that may use some combination of hiring ($200 per worker), laying of ($100 per worker), part-time labour ($8 per unit, maximum of 20 units per month, must use for at least three consecutive months), and overtime ($9 per units maximum of 25 per month). The ending inventory in month 9 should be zero with no backorders at the end. Compute the total cost.