First, let's use the following formula about the margin error.
But, we use n to find the degrees of freedom.
Using a calculator, we get a critical value t-score of 3.5.
Now we can find the margin error.
Then, we form the confidence interval using the mean.
[tex]\begin{gathered} 13.2-4.95
Therefore, the confidence interval is 8.25 < m < 18.15.