Classify the total costs of each of the following as variable, fixed, mixed, or step.

(a) Maintenance costs of a university.

(b) Rates.

(c) Rent of a photocopier charged as a fixed amount per month plus an additional charge per copy.

(d) Cost of goods sold in a book shop.

(e) Salaries paid to part-time lecturers in a college as the number of courses offered varies.

(f) Wood used by a house-building company.

(g) The costs of operating a research department.

(h) The costs of hiring a dance hall for three hours.

(i) Typing paper used in the typing pool.
(j) Electric power in a restaurant.