A company that makes cola drinks states that the mean caffeine content per​ 12-ounce bottle of cola is 50 milligrams. You want to test this claim. During your​ tests, you find that a random sample of thirty​ 12-ounce bottles of cola has a mean caffeine content of 50.9 milligrams. Assume the population is normally distributed and the population standard deviation is 7.5 milligrams. At α=0.05​, can you reject the​ company's claim?

a. Find the critical​ value(s). Select the correct choice below and fill in the answer box within your choice.
b. Find the standardized test statistic.