Answer:
$20
Explanation:
Marginal cost is the extra cost incurred in order to produce and additional unit of a product.
Marginal product is an additional unit obtained from an extra unit of input.
From the question;
Variable cost per unit of labor = Marginal cost of labor = $20
Marginal product of labor = $2
Therefore, the marginal cost of production when the firm hires 5 workers is variable cost per unit of labor which is $20.