16. Describe how fixed costs respond to changes in the activity level per unit and in total. (18) 17. If a company has excess capacity, under what situations would the company accept a special order for less than the current selling price? (20) 18. What is the implication that a project's payback period is greater than its expected useful life? (25) 19. How is contribution margin calculated? (18) 20. What do product costs consist of? (14) What are examples of period costs? (14)