help please

4. [14.42 Points] DETAILS BBUNDERSTAT12 7.2.0135. MY NOTES | ASK YOUR TEACHER The method of tree ring dating gave the following years AD. for an archaeological excavation site. Assume that the population of x values has an approximately normal distribution. 1.278 1.313 1.313 1.292 1.268 1.316 1.275 1.31? 1.275 I USE SALT (a) Use a calculator with mean and standard deviation keys to find the sample mean year} and sample standard deviation 5. (Round your answers to four decimal places.) AD. yr X S (b) Find a 90% condence interval for the mean of all tree ring dates from this archaeological site. (Round your answers to the nearest whole number.) lower limit AD. upper limit AD