Step 1 :\( n = 16 \)
Step 2 :\( \overline{x} = \frac{1}{16}(14 + 12 + 18 + 14 + 14 + 16 + 17 + 11 + 12 + 15 + 12 + 12) = 14 \)
Step 3 :\( s = \sqrt{\frac{1}{15}((14-14)^2 + (12-14)^2 + (18-14)^2 + (14-14)^2 + (14-14)^2 + (16-14)^2 + (17-14)^2 + (11-14)^2 + (12-14)^2 + (15-14)^2 + (12-14)^2 + (12-14)^2 )} \) = \sqrt{6.27} \)
Step 4 :\( \frac{s}{\sqrt{n}} = \frac{\sqrt{6.27}}{\sqrt{16}} = 0.6175 \)
Step 5 :\( t^{*} = 1.753 \) (based on 90\% confidence level and \( n-1 = 15 \) degrees of freedom)
Step 6 :\( \text{CI }= (\overline{x} - t^* \frac{s}{\sqrt{n}}, \overline{x} + t^* \frac{s}{\sqrt{n}}) = (14 - 1.753(0.6175), 14 + 1.753(0.6175)) = (13.08, 14.92) \)