please explain your answer well and the formulas you use

39. The amount of beryllium in a substance is often determined by the use of a photometric filtration method. If the weight of the berylium is , then the value given by the photometric filtration method is normally distributed with mean 11 and standard deviation ?. A total of eight independent measurements of 3.180 mg of beryllium gave the following results 3.166, 3.192, 3.175, 3.180,3.182,3.171,3.184,3.177 Use the preceding data to (a) estimated (b) find a 90 percent confidence interval estimate of