Sal's International is a popular haircutting and styling salon near the campus of the University of New Orleans. Four barbers work full-time and spend an average of 15 minutes per customer. Customers arrive throughout the day at an average rate of 12 each hour. All arriving customers are assigned a waiting number. Arrivals tend to follow the Poisson distribution, while service time is exponentially distributed. Assuming an infinite population source, determine the following:
1. What is the average number of customers in the salon?
2. What is the average time that a customer spends in the salon?
3. What is the average time a customer spends waiting to be attended?
4. What is the average number of customers waiting to be attended?