A university has 20,000 students out of which 15,000 are undergraduate students and 5000 are graduate students. You have selected a stratified sample from the population of students at the university with undergraduate students and graduate students as the two strata. For each member of your sample, you recorded how much money they spent on books in 2022. The results are as follows: (1) Undergraduate students: n1 = 400, X-bar-1 = 600, s1 = 300 (2) Graduate students: n2 = 100, X-bar-2 = 400, s2 = 240 Let denote the average amount of money a student at the university spent on books in 2022. (This average is the average of the whole population of students, graduate students and undergraduate students, combined.) Construct a 99% confidence interval for