Consider now the customer lines forming in front of the $3$ ordering counters. Assume the customer arrival process has the baseline average demand rate of $25$ customers per hour, with a coefficient of variation of $1\mathrm{.}2$ for the inter$-$arrival times. Assume also that the service time for each customer at any one of the ordering counters has an average of $6$ minutes and a coefficient of variation of $1\mathrm{.}1.$

a$.$ What is the average fraction of time when staff at the ordering counters are idle?