19. (16 points) A sample of 4 diesel trucks gave the following fuel mileages (in miles per gallon): 4.56, 4.46, 4.89, 4.77 (a) (6 points) Find the sample mean (2 points) and sample standard deviation (4 points) of the fuel mileages. (b) (10 points) Assume that fuel mileages for this type of truck are approximately normally distributed, and find a 98% confidence interval for the population mean fuel mileage for this type of truck