A researcher wants to estimate the average life expectancy for Wisconsinites. She takes a random sample of 50 Wisconsinites and finds that the average life expectancy is 76.7 years. Also, she assumes that the population standard deviation is 4.5 years.c) Construct a 95% confidence interval for the mean life expectancy of all Wisconsinites (Hint: See slide 14 in the part 1 lecture. Format of a confidence interval is x z_(/2) /n . Calculate the lower and upper limit numbers in Excel.)