A post office clerk operates with $75\%$ utilization. The coefficient of variation for the service process is $0\mathrm{.}6$ and the coefficient of variation of the arrival process is $0\mathrm{.}9.$ The average processing time is $4$ minutes. What is the average time a customer spends in the system according to the single$-$server queue model?

Multiple Choice

$7\mathrm{.}02$ minutes

$4$ minutes

$11\mathrm{.}02$ minutes

$3\mathrm{.}51$ minutes