Please could I be shown how to solve this with the workings as well

The number of carbohydrates (in grams) per 8-ounce serving of yogurt for each of a random selection of brands is listed below. Estimate the true population variance and standard deviation for the number of carbohydrates per 8-ounce serving of yogurt with 95% confidence. Assume the variable is normally distributed. 15 17 20 23 25 25 33 34 35 38 39 41 41 42 42 43 a. Calculate the degrees of freedom (12 mark/work, 1/2 mark/answer) 1) b. Calculate the mean (12 mark/work, 1/2 mark/answer with 2 decimals) (2) c. Calculate the sample variance (1 mark/work, 1 mark/answer with 2 decimals) (2) d. Calculate a for right e. Calculate a for left (1/2 mark/work, 1/2 mark/answer) (1/2 mark/work, 1/2 mark/answer) (1) f. What is Xright ( 1/2 mark/answer) g. What is Xleftt ( /2 mark/answer)