4.
Water bill, which entails a flat fee for the first 10,000 gallons used and then an increasing unit cost for every additional 10,000 gallons used
5.
Availability of quantity discounts, where the cost per unit falls as each price break is reached
6
Depreciation of office equipment
.
7
Cost of sheet steel for a manufacturer of farm implements
.
8.
Salaries of supervisors, where one supervisor is added for every 12 phone solicitors