At a single$-$phase, multiple$-$channel service facility, customers arrive randomly. Statistical analysis of past

data shows that the interarrival time has a mean of $20$ minutes and a standard deviation of $4$ minutes. The

service time per customer has a mean of $15$ minutes and a standard deviation of $5$ minutes. The waiting cost is

$$200$ per customer per hour. The server cost is $$25$ per server per hour. Assume general probability

distribution and no buffer capacity restriction. Find the cost per hour, average waiting time, and average flow time for one server if the probability

distributions for the interarrival time and service time are assumed to be exponential and the mean values

remain the same. The cost data remain the same. Use manual calculations. $($Ans: Cost per hour$=$$$475\mathrm{.}00,$

Waiting time$=45\mathrm{.}00$ min, Flow time$=60\mathrm{.}00$ min$).$