To promote its reputation for fast service, Earl's While U Wait Automotive Tune up Shop promises to reduce a customer's bill by $0.50 for every minute the customer must wait until his or her car's tune up is finished. The inter arrival time for Earl's customers has an exponential probability distribution with a mean arrival rate of 4 customers per hour. We assume that a mechanic earns $20 per hour and can perform a tune up in a time that has an exponential probability distribution with a mean tune up rate of 2 cars per hour. Let us call such a mechanic a class B mechanic. In comparison to a class B mechanic, a class A mechanic earns an hourly salary of $35 per hour and can perform a tune up in a time that has an exponential probability distribution with a mean tune up rate of 3 cars per hour. Suppose in this exercise that Earl is considering a staff consisting of either two class A mechanics or three class B mechanics. Should Earl hire two class A mechanics or three class B mechanics?