Suppose the figure below shows Luke's demand curve for check-ups along with the supply curve for check-ups. 
What is the marginal cost of one extra check-up?
Definitions:
Bottler
A company or entity that places beverages into bottles for distribution and sale.
Restatement Second Torts
A legal treatise that summarizes the general principles of American tort law, including definitions of torts and the standards of liability.
Business Visitor
An individual who enters a premises for purposes related to business or commerce, often accorded certain legal protections.
Public Invitee
A person who is invited to enter or remain on property for a purpose directly or indirectly connected to business dealings with the proprietor.
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