For a single$-$server system, the mean arrival rate is $2$ customers per hour, and the average number of customers observed waiting in queue is $3\mathrm{.}2$ customers.

Additionally, you learn the service rate is $2\mathrm{.}5$ customers served per hour.

$3c$ : What is the expected time, in hours, a customer will spend in the system?

$($use two decimal place accuracy with rounding$)$