The correct answer is B (29).

Explanation:

• For a paired comparisons test, the t-statistic has $n - 1$ degrees of freedom, where $n$ is the number of paired observations.
• Here, $n = 30$, so the degrees of freedom are $30 - 1 = 29$.

Why not A or C?

• A (28) is incorrect because it assumes $n - 2$ degrees of freedom, which is not applicable for a paired test.
• C (58) is incorrect because it represents the degrees of freedom for a hypothesis test concerning the equality of means of two independent samples, calculated as $n_1 + n_2 - 2$.