A single$-$phase waiting$-$line system meets the assumptions of constant service time or M$/$D$/1.$ Units arrive at this system every $10$ minutes on average. Service takes a constant $4$ minutes. The average length of the queue $$ is A$)0\mathrm{.}4$ B$)0\mathrm{.}133$ C$)4\mathrm{.}167$ D$)4\mathrm{.}583$ Answer: B$)0\mathrm{.}133$