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 10 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 negative exponential.

The cost of the clerk is 12 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.

​a) The average time that catalog customers must wait before their calls are transferred to the order clerk​ = ______ minutes​(round your response to two decimal​ places).
b) The average number of callers waiting to place an order​ =
c) The total present cost per hour​ =
d) After adding the second​ clerk, the average time that catalog customers must wait before their calls are transferred to the order clerk​ = ____ minutes
e) After adding a second clerk to take calls and assuming that the​ store's cost would be the same ​$12 per hour. The total cost​= $____ per hour
f) By hiring the second​ clerk, the total per hour cost change for​ Janson's = $____ per hour