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A firm needs to produce 100 units of its output using labour and machines. At its current input combination, the marginal rate of substitution is 2. It faces a wage rate of $10 and a cost of machine equal to $20 per unit The firm is not minimizing the cost of producing 100 units because, by hiring one more unit of labour, it can reduce its production cost by __. while still producing 100 units. Q a. $50 O b. $20 O c. $30 O d. $10