You have two milling machines dedicated to production of a single product. Each batch requires a setup time of 15 minutes per batch, the processing time per unit is 4 minutes, and the batch size is set at 70 units. Each machine processes an entire batch at one time. The machines are staffed 8 hours per day. If the average arrival rate to the machines is 2.5 batches per day, what is the average utilization of the machines?