How do you determine that the test statistic region is 0.215 ? The p-value for the two-tailed test of H0 : 1 = 0 is the probability (under H0) of obtaining a test statistic less than t = 1.257 or greater than t = 1.257. We have 51 observations, so we are working with a t distribution with 49 degrees of freedom. Given this probability distribution, the probability of obtaining a test statistic in this region is 0.215. So, we would only reject the hypothesis b1 = 0 at the 21.5% level.