A server operates with $80\%$ utilization. The coefficient of variation for the service process is $0\mathrm{.}5$ and the coefficient of variation of the arrival process is $1.$ The average

processing time is $3$ minutes. What is the average time a customer spends in the system according to the single$-$server queue model?

A$.7\mathrm{.}5$ minutes

B$.10\mathrm{.}5$ minutes

C$.3$ minutes

D$.3\mathrm{.}75$ minutes