Vehicles begin to arrive at a zoo at 8:45 A.M. at a λ of six vehicles per minute. At 9:00 A.M. onward λ changes to four vehicles per minute. If the park opens at 9:00 A.M. If the average delay per vehicle is to be 9 minutes or less (measured from the first vehicle arrival until dissipation of the queue). Assume a D/D/1 queuing model, Calculate the lowest departure rate required to attain this?