8) How much does a sleeping bag cost? Let's say you want a sleeping bag that should keep you warm in temperatures from 20F to 45F. A random sample of prices ($) of sleeping bags for this temperature range is shown below. Assume that the prices of sleeping bags follow normal distribution with standard deviation = 30. 80 90 100 120 75 105 95 105 60 110 37 30 23 100 110 120 95 90 60 70 a) Calculate the sample mean. 7 b) Calculate 95% confidence interval for the true average price (u) of all sleeping bags of this kind. c) Interpret the confidence interval obtained in above part. d) Does the interval suggest that $65 is a plausible value for the average price? Justify you answer.