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

In a queueing system, customers arrive once every $6$ seconds $($standard deviation $=8)$ and services take $4$ seconds $($standard deviation $=5\mathrm{.}9).$

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

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