the organizers of the conference convention centre are evaluating the possibility of setting up a computer area where attendees can check their email on the computer provided by the organization. There will be one common queue for all computers, and only one person uses a computer at a time. On average, there are 15 attendee arrivals per hour, the standard deviation of the time between arrivals is 4, and the average time a person spends on the computer is 10 minutes (with a standard deviation of 3). To ensure that waiting times are not too long, the organizers want to ensure that the utilization of the computer doesn't exceed 90%. At least (at the minimum) how many computers do they need to have?