Assume you are working with the results of a research situation based on a matched sample design involving 15 participants (the same participants in a before/after test situation). The mean difference (D) = 14.66, with an estimate of the standard error of the mean difference (SD) = 5.21. Assume that you're working at the .05 level of significance. a. Formulate an appropriate null hypothesis. b. Calculate t. c. Identify the critical value.