In an M$/$M$/1$ queue with a service rate of $12$ customers per hour and an arrival rate of $4$ customers per hour, what is the average waiting time in the system?

Question $19$ options:

$0\mathrm{.}167$ hours

$0\mathrm{.}25$ hours

$0\mathrm{.}375$ hours

$0\mathrm{.}5$ hours

None of the above