$($b$)$ Draw a logical model $($network$)$ for the following system. Specify all the details on the network.

Parts arrive at a CNC for machining. The interiarrival time is exponentially distributed with mean value

$8$ minutes. The parts wait for processing on a first$-$in first$-$out basis. The processing time per part is

exponentially distributed with mean processing time $3$ with probability $0\mathrm{.}4.$ Rejected parts are placed

in the queue of unprocessed parts, after a delay of $15$ seconds.