7. A self-service car wash has 4 washing stalls. When in a stall, a customer may choose from among three options: rinse only; wash and rinse; and wash, rinse, and wax. Each option has a xed time to complete: rinse only, 3 minutes; wash and rinse, 7 minutes; wash, rinse, and wax, 12 minutes. The owners have observed that 20% of customers rinse only; 70% wash and rinse; and 10% wash, rinse, and wax. There are no scheduled appointments, and customers arrive at a rate of about 34 cars per hour. There is room for only 3 cars to wait in the parking lot, so, currently, many customers are lost. The owners wants to know how much more business they will do if they add another stall. Adding a stall will take away one space in the parking lot. Develop a queuing model of the system. Estimate the rate at which customers will be lost in the current and proposed system. Carefully state any assumptions or approximations you make