Problem: The manager of a grocery store in the retirement community of Sunnyville is interested in providing good service to the senior citizens who shop in her store. Currently, the store has a separate checkout counter for senior citizens. On average, 25 senior citizens per hour arrive at the counter, according to a Poisson distribution, and are served at an average rate of 30 customers per hour, with exponential service times characteristics. On average, how long does a senior citizen wait in line before being served?