A new full-service, attendant-staffed fuel and car service station on Interstate 95 will service only northbound cars. The manager estimates that customers will arrive every 4 minutes and will require 6 minutes to be served at the pump. How many pumps should be installed if the manager desires a utilization factor of 0.75? What percent of the time will the pumps be idle? Assume that the coefficients of variation of both the inter-arrival times and the service times are equal to 1.