Let us consider this queueing system: There are two cook in a kitchen at a restaurant. The entire order of a customer is provided by only one cook (no collaboration is possible). The time between customer orders follows an exponential distribution with the mean of 15 minutes. When there are n orders (under processing or waiting), the time to fulfil customers orders (cooking time) follows an exponential distribution with the mean of (20-5n) minutes. For example, if there are two orders at the kitchen (two under processing and no waiting), the average processing time is 10 min. If both cooks are busy at the kitchen, no new orders are accepted from customers. Determine the average utilization (percentage of a cooks busy time) of each cook.