Shards of clay vessels were put together to reconstruct rim diameters of the original ceramic vessels found at the Wind Mountain archaeological site. A random sample of ceramic vessels gave the following rim diameters (in centimeters):
15.9 13.4 22.1 12.7 13.1 19.6 11.7 13.5 17.7 18.1
(a) Use a calculator with mean and sample standard deviation keys to verify that  ≈ 15.8 cm and s ≈ 3.5 cm.
(b) Compute an 80% confidence interval for the population mean μ of rim diameters for such ceramic vessels found at the Wind Mountain archaeological site.