Janson's Department Store in? Stark, Ohio, maintains a successful catalog sales department in which a clerk takes orders by telephone. If the clerk is occupied on one? line, incoming phone calls to the catalog department are answered automatically by a recording machine and asked to wait. As soon as the clerk is? free, the party who has waited the longest is transferred and serviced first. Calls come in at a rate of about 12 per hour. The clerk can take an order in an average of 3.0 minutes. Calls tend to follow a Poisson? distribution, and service times tend to be exponential. The cost of the clerk is ?$8 per? hour, but because of lost goodwill and? sales, Janson's loses about ?$30 per hour of customer time spent waiting for the clerk to take an order. The average number of callers waiting to place an order? = ____ callers (2 decimals)