Skyline Agency is compensated through a markup charge. What does that mean?

Question $10$ options:

a$)$

Skyline charges the client an hourly rate for the services provided by its employees.

b$)$

Skyline contracts out its services and then charges the client an agreed$-$upon percentage above what those contracted services cost.

c$)$

Skyline is paid a variable amount based upon the achievement of certain objectives, as measured through sales.

d$)$

Skyline receives an agreed$-$upon percentage of the amount that the client spends on media.