Answer:
1. E. Reject H0 if t > 1.721
2. B. 1.679
Explanation:
This would be a hypothesis test for the difference between two means. In the way that the alternative hypothesis.
The critical value depends on the significance level, the test type (one-tail or two-tailed) and the degrees of freedom.
This is a t-test type, so the statistic is t and not z. In the way that the alternative hypothesis, where only matter if the mean A is significantly bigger than mean B, this is a one-tail test.
The degrees of freedom can be calculated as:

Then, for a one-tail t-test, with significance level of 0.05 and 21 degrees of freedom, the critical value is t=1.721.
The standard deviation of the difference between the two means can be calculated as:
