The following table shows the average number of words understood by later-born and first-born one-year-old children from two random samples. Assume the population variances of the number of words understood are equal. Use the table to complete parts a through c. Later-Born First-Born Sample mean 434.6 556.0 Sample standard deviation 130.3 131.9 Sample size 13 13 a. Construct a 99% confidence interval to estimate the difference between the average number of words understood by first-born and later-born one-year-old children. The 99% confidence interval is (]. D (Round to two decimal places as needed.)