OK I so need help....I have tried to solve this but I can't. I thought if I had the formula I could just plug in the numbers. I just do not understand how 5.83% and 9.81% is the answer.... I get 7.87% and 7.76%....using 7.82% as the average meanwhat am I doing wrong???

This is the problem, I have been asked to solve construct a 93% confidence interval for the MEAN of the column 'Annual % ROI'.We do not know the population standard deviation. Here is the data I have been given n= 20 colleges

7.70% 20 colleges with %

8.40%

7.80%

7.40%

7.30%

7.20%

7.00%

7.10%

7.00%

7.20%

7.00%

7.00%

7.50%

6.90%

6.70%

8.10%

9.10%

10.10%

9.90%

10.00%

PLEASE HELP!!!