Final answer:
Marginal cost is the additional cost of producing one more unit of output.
Step-by-step explanation:
Marginal cost is the additional cost of producing one more unit of output. It is calculated by dividing the change in total cost by the change in quantity. For example, if the total cost increases by $80 when producing an additional 20 haircuts, the marginal cost would be $4 per haircut. The marginal cost curve is generally upward-sloping due to diminishing marginal returns, meaning that producing additional units becomes more costly.