9. At one of the clinics, an employee calls patients to remind them of their upcoming appointments and to verify their insurance. The number of patients to call follows a Poisson distribution with a mean of six per hour. The time it takes to complete a call follows a normal distribution with a mean of 4 minutes and a standard deviation of 1 minute.

a. On average, how many calls wait to be processed?

b. On average, how long does a call spend in the system (waiting and being processed)?

c. What proportion of the time is the clerk free to do other tasks?