Additional Algo $16-7$ Queues when Demand and Service Rates Are Variable $-$ One Server

In a queueing system, customers arrive once every $3$ minutes $($standard deviation $=4)$ and services take $2$ minutes $($standard deviation $=6\mathrm{.}3).$

What is the average time a customer will spend in the system $($in minutes$)?$

Note: Do not round intermediate calculations. Round your answer to $3$ decimal places.