I got the answers to this question except for the last part.

In a study to determine how much time children spend watching television, a researcher obtained the following data from a number of children:

39.7 23.6 20.6 33 35.3 30.8 22.1 28.4 20.5 27.2 29.3 23.4

a)find the 95% confidence interval for the mean number of hours children spent watching television.

b)find the 95% confidence interval for the standard deviation of the hours children spent watching television.

c)what assumptions do you need to make to answer a) and b)?

I've got the answer for Part a which is23.94<mu<31.71, and part b 4.23<sigma<10.38.

but I don't know how to answer the last part.

Thank you for your help!