A major department store chain is interested in estimating the mean amount its credit card customers spent on their first visit to the chain's new store in the mall. Fifteen credit card accounts were randomly sampled and analyzed with the following results = $50.50 and S = 20. Construct a 95% confidence interval for the mean amount its credit card customers spent on their first visit to the chain's new store in the mall assuming that the amount spent follows a normal distribution.
i) Determine the distribution to be used (z or t)
ii) Find degrees of freedom (n-1), confidence level (1-?), and critical value/2?t
iii) Construct the interval using the above formula