what is C and D? thank you!

An office employs several clerks who create documents and has one operator who enters the document information in a computer system. The group creates documents at a rate of 20 per hour. The operator can enter the information with an average exponentially distributed time of 2 minutes. Assume the population is infinite, arrivals are Poisson, and queue length is infinite with FCFS discipline. a. Calculate the percentage utilization of the operator. (Round your answer to 2 decimal places.) b. Calculate the average number of documents in the system. (Round your answer to 1 decimal place.) c. Calculate the average time in the system. (Round your answer to 1 decimal place.) c. Calculate the average time in the system. (Round your answer to 1 decimal place.) d. Calculate the probability of four or more documents being in the system. (Round your intermediate calculations to 3 decimal places and final answer to 1 decimal place.)