The distribution of heights for a population of individuals between the ages of 12 and 40 who suffer from fetal alcohol syndrome is approximately normal with unknown mean . A random sample of 31 patients is selected from the underlying population; the mean height for these individuals is =147.4 cm and a sample standard deviation s=6. a. Construct a 95% confidence interval for the mean . b. Construct a 99% confidence interval for the mean . c. Can we omit the normal assumption?