The method of tree ring dating gave the following years A. D. for an archaeological excavation site. Assume that the population of x values has an approximately normal distribution.1229 1257 1313 1201 1268 1316 1275 1317 1275(a) Use a calculator with mean and standard deviation keys to find the sample mean year x and sample standard deviation s. (Round your answers to the nearest whole number.)x = A. D.s = yr(b) Find a 90% confidence interval for the mean of all tree ring dates from this archaeological site. (Round your answers to the nearest whole number.)lower limit A. D.upper limit A. D.