I'm having problems with the advanced statistics formula for obtaining a t obt statistic. I'm not sure how to do this for a problem with two lists of numbers.

A professor of women's studies is interested in determining if stress affects the menstrual cycle. Ten women are randomly sampled for an experiment and randomly divided into two groups. One of the groups is subjected to high stress for two months while the other lives in a relatively stress-free environment. The professor measures the menstrual cycle (in days) of each woman during the second month. The following data are obtained.

High stress

20

23

18

19

22

Relatively stress free

26

31

25

26

30