A linguist wants to compare the writing styles in two magazines and one measure is the number

Question:

A linguist wants to compare the writing styles in two magazines and one measure is the number of words per sentence. On the basis of 50 randomly selected sentences from each source, she finds
Magazine 1 n1 = 50 = 12.6 s1 = 4.2
Magazine 2 n2 = 50 = 9.5 s2 = 1.9
Determine a 98% confidence interval for the difference in mean number of words per sentence.