Fanning Training Services $($FTS$)$ provides instruction on the use of computer software for the employees of its corporate clients. It offers courses in the clients$$ offices on the clients$$ equipment. The only major expense FTS incurs is instructor salaries; it pays instructors $$5,600$ per course taught. FTS recently agreed to offer a course of instruction to the employees of Novak Incorporated at a price of $$410$ per student. Novak estimated that $20$ students would attend the course. FTS sells a custom wood plaque to students who complete the training course. Due to the custom nature of these plaques, FTS has to produce them in advance based on the estimated number of students to be enrolled in the course. Any plaques made for students who do not end up completing the course will be discarded. Prior to the first class, FTS pre$-$ordered $20$ plaques based on the client's estimate of the number of people who would attend the course. FTS will only have $20$ plaques to offer students regardless of whether enrollment is below or above expectations due to them having to be made in advance of the course. Each plaque costs $$31$ and is sold to students who complete the course for $$48.$

Calculate the cost of plaques in total and per unit, assuming that $17,20,$ or $22$ students complete the course.

Classify the total cost of plaques as fixed or variable relative to the number of students attending the course.