A random sample of 20 department stores of Maximus Pty Ltd was selected as part of a study on the average advertising expenses, and the expense amounts were recorded for each individual store in the sample.

The sample average advertising expense was found to be = 65.9 ($000).

a. Assuming that the advertising expenses is normally distributed with a sample standard deviation of 8.5($000), calculate a 95% confidence interval for the mean advertising expenses.