In a M/M/I queuing system, expected waiting time of a unit that actually waits is given y?

• A. \[\frac{\lambda }{{{\mu }^{2}}(\mu -\lambda )}\]
• B. \[\frac{\lambda }{\mu -\lambda }\]
• C. \[\frac{1}{\mu -\lambda }\]
• D. \[\frac{\lambda }{{{\mu }^{2}}(\mu -\lambda )}\]