When the sample size is 19, a two-sided 95.0% confidence interval for a single mean will have an interval that extends no more than 1.5 from the observed mean, assuming that the true standard deviation is 3.25 and that the confidence interval is based on the t statistic. The "typical" mean is 14 hours and the 95% confidence interval around 12.5 hours is 11hours to 14 hours.