Cost ($) 7.42 6.29 5.83 6.50 8.34 9.51 7.10 6.80 5.90 4.89 6.50 5.52 7.90 8.30 9.60 8.18 The file [Fast Casual] contains the amount that a sample of 15 customers spent for lunch ($) at a fast casual restaurant: a. Construct a 95% confidence interval estimate for the population mean amount spent for lunch ($) at a fast casual restaurant. b. Interpret the interval constructed in (a). c. What assumption must you make about the population distribution in order to construct the confidence interval estimate in (a)? d. Do you think that the assumption needed in order to construct the confidence interval estimate in (a) is valid? Explain.