$.$ The workers at a factory with $2$ inspectors must carry their work to the quality control

department before the product is released. They arrive at a rate of approximately $20$

workers$/$hour$,$ following a Poisson process. The time to inspect a part follows an exponential

distribution with a mean of $4$ minutes.

a$)$ Percent of time that the server is idle $($Po$)[20\mathrm{.}0\%]$

b$)$ Number of customers waiting in the queue $($Lq$)[1\mathrm{.}1]$

c$)$ Average time that customers are in the system $($Ws$)[7\mathrm{.}2$ minutes$]$

d$)$ Average waiting time of the customers in the queue $($Wq$)[3\mathrm{.}2$ minutes$]$