Based on the selling price and market wage rate, the number of workers she should hire to maximize profit is 5 workers.
This is the point where the Marginal revenue will be equal to the marginal cost which is the wage rate of $40 in this scenario.
4 workers: 5 workers
= 21 units x 10 per unit = 25 x 10
= $210 = $250
= Revenue at 5 workers - Revenue at 4 workers
= 250 - 210
= $40
This is equal to the marginal cost so 5 workers is the profit maximizing quantity.
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