if I test coefficient GDP, how do I know the degree of freedom = n-1 or n-1-k? if alpha in this case 10% , how do I know it is two tails or one tail test in order to look at the table 5% or 10%. thank you so much for your comments

sales =

10.2 +

(4.6 × CPI) +

(5.2 × IP) +

(11.7 × GDP)

(5.4)

(3.5)

(5.9)

(6.8)

A 90 percent confidence interval for the coefficient on GDP is:

**A)** –1.5 to 20.0. **B)** –1.9 to 19.6. **C)** 0.5 to 22.9.

**Your answer: C was correct!**

A 90% confidence interval with 176 degrees of freedom is coefficient ± t_{c}(s_{e}) = 11.7 ± 1.654 (6.8) or 0.5 to 22.9.