You wish to test H 0 : μ d = 0 versus H a : μ d < 0 at a significance level of 0.10. For the context of this problem, μ d = μ 2 − μ 1 where the first data set represents a pre-test and the second data set represents a post-test. You obtain pre-test and post-test samples for n d = 28 subjects. The average difference (post - pre) is ¯ x d = − 4.3 with a standard deviation of the differences of s d = 45.5 . What is the test statistic?