Five Lakes Video, a small video rental store in Cleveland, is open 24 hours a day, and --- due to its proximity to a prestigious business school --- experiences customers arriving around the clock. A recent analysis indicates that on average, 30 customers arrive every hour, with a standard deviation of the inter-arrival time being 2 minutes. This arrival pattern stays true regardless of the time of the day. The checkout is currently operated by one employee, who needs an average of 1.7 minutes to check out a customer. The standard deviation of this check-out time is 3 minutes. As a special service, the store offers free popcorn and sodas for customers waiting in line at the checkout desk. (Note: the person that is being served is too busy with paying to eat or drink.) The store owner estimates that, for every minute a customer waits in line, it costs the store 75 cents because of the consumed food. If the goal of the store is to minimize cost, what is the optimal number of employees at checkout