Take into account that the confidence interval is given by:
![\mu\pm Z\cdot\frac{s}{\sqrt[]{n}}](https://img.qammunity.org/2023/formulas/mathematics/high-school/a6fy2t3lb42h1p2lqjd8t1s0sjqtysqa1y.png)
where
μ: mean = 18.2
Z: z-value for 95% confidence = 1.96
s = 18.2
n: sample = 86
Replace the previous values into the confidence interval formula:
![\begin{gathered} 18.2+1.96\cdot\frac{18.2}{\sqrt[]{86}} \\ 18.2\pm3.85 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/3e0ejf2mipryjd2mph0izcn3hf8c0lkti6.png)
Hence, the confidence interval is:
CI = (18.2 - 3.85 , 18.2 + 3.85) = (14.35 , 22.05)
Rounded to the nearest whole number the confidence interval is:
CI = (14 , 22)