Show me the steps to solve $7.$ Kay Nein is a dentist and provides Rusty Clutch with $$800$ of dental services in exchange for Rusty repairing Kay$$s car. Kay will recognize how much gross income on this exchange?

a$.$ $$0$

b$.$ The out$-$of$-$pocket cost of the car repair $($parts$)$

c$.$ The out$-$of$-$pocket costs for the dental work

d$.$ The market value of the services exchanged $($$$800)$