The Western blot assay is a blood test for the presence of HIV. It has been found that this test sometimes gives false positive results for HIV. A medical researcher claims that the rate of false positives is 2%. A recent study of 300 randomly selected U.S. blood donors who do not have HIV found that 3 received a false positive test result. At a = 0.05, is there enough evidence to reject the researcher's claim? (Adapted from Centers for Disease Control and Prevention) In Exercises 53-56, find the critical value(s) for the indicated x-test for a population variance, sample size n, and level of significance a.