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Consider a single$-$server queuing system $($with Poisson arrivals and exponential service times$).$ If the arrival rate is $30$ units per hour, and each customer takes $30$ seconds on average to be served, what is the average length of the line?

$\backslash$table$[[0\mathrm{.}166],[0\mathrm{.}083],[1\mathrm{.}03],[0\mathrm{.}333],[-1\mathrm{.}03]]$