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