An advertisement for a major home appliance manufacturer claims that its repair personnel are the loneliest in the world because its appliances require the smallest number of service calls. To examine this claim, a researcher drew a random sample of 100 owners of 5-year-old washing machines. The number of service calls made in the 5-year period were recorded. Find the 90% confidence interval estimate of the mean number of service calls for all 5-year-old washing machines.