You would like to construct a 99% confidence interval to estimate the population mean PCB (Polychlorinated biphenyl) Ievel in white croaker fish from the San Francisco Bay: The random sample we select has a mean of 637 parts per million and a standard deviation of 52 parts per milion. (a) What is the best point estimate, based on the sample, to use for the population mean? parts per million (b) For each of the following sampling scenarios, determine which distribution should be used to calculate the critical value for the 99% confidence interval for the population mean. (In the table, z refers to a standard normal distribution, and t refess to a tifstnbution.) (b) For each of the following sampling scenarios, determine which distribution should be used to calculate the critical value for the 99% confidence interval for the population mean. (In the table, Z refers to a standard normal distribution, and t refers to a (distnbution.)