An assembly line can produce 90 units per hour. The lines hourly cost is $4500 on straight time (the first 8 hours). Workers are guaranteed a minimum of 6 hours. There is a 50% premium for overtime, however, productivity for overtime drops by 5%. What are the average and marginal costs per unit for the following daily quantities?

a. 450

b. 600

c. 720

d. 900