The answer is C) marginal cost. The term "marginal cost" refers to the cost added by producing one additional unit of a product or service, in this case $10. Retail price refers to the price that a business charges for a good sold to a consumer, including the manufacturing cost and markup value. Net benefit is defined as the total economic benefit received from a change in the state of a good or service, measured by the sum of consumer surplus plus producer surplus, less any costs associated with the change.