It takes a phlebotomist takes 15 minutes to complete a blood draw. The supplies for each draw takes cost $4, and the phlebotomist earns $20 per hour. The phlebotomy lab is designed to accommodate 20,000 draws per year. Its rent is $80,000 per year. What are the average and incremental costs of a blood draw when the volume is 20,000? $10,000? What principle does the calculation illustrate? (Ctrl)