sing R programming and mention the source like book,website from which it is done and how it is done

In a study on cholesterol levels a sample of 12 men was chosen. The plasma cholesterol levels (mmol/L) of the subjects were as follows:

6.0,6.4,7.0,5.8,6.0,5.8,5.9,6.7,6.1,6.5,6.3,5.8

(a) Estimate the variance of the plasma cholesterol levels with a 99% confidence interval.

(b) What assumptions did you make about the sample in order to make your estimate?