In the context of hypothesis testing using a paired t-test, if n is the number of pairs in the two related samples, what is the degrees of freedom?

In a moderately skewed distribution, if Mean = 12 and Median = 8, then using Empirical relation (Mode = 3 Median - 2 Mean), what is the value of Mode?

If 4y - 5x = 15 is the regression line of y on x and the coefficient of correlation between x and y is 0.75, what is the value of the regression coefficient of x on y (bxy)?