During the early morning hours, customers arrive at a branch post office at an average rate of 33 per hour (Poisson), while clerks can provide services at a rate of 11 per hour. If clerk cost is $36.08 per hour and customer waiting time represents a cost of $41 per hour, how many clerks can be justified on a cost basis

a.

7

b.

4

c.

5

d.

6

e.

8