9.4.2 Consider the preemptive priority queue of Section 9.4.5 and suppose that the arrival rate is  D 4 per hour. Two classes of customers can be identified, having mean service times of 12 min and 8 min, and it is proposed to give one of these classes priority over the other. Recommend which class should have priority.

Be explicit about your criterion and justify your answer. Assume that the two classes appear in equal proportions and that all service times are exponentially distributed.