One approach to investigating the consequences of a major oil spill in the Gulf of Mexico is to look at the amount of heavy metals that have been incorporated in the shells of oysters. Oysters continually build their shells, and if vanadium, cobalt, or chromium from the oil are incorporated in the shells, this might seriously effect the food chain. Suppose that, from a sample of size n = 12 shells, the scientists obtain the summary statistics  = 45 ppm and s = 5.9 ppm for the amount of heavy metals in the oyster shells. Assuming that the population distribution is normal, obtain a 95% confidence interval for the mean amount of heavy metals in oyster shells.