ANSWER:
(25.46, 28.34)
Explanation:
Given:
n (sample size) = 50
m (mean) = 26.9
sd (standard deviation) = 6.06
The formula for the confidence interval is:

The t- critical value at the 90% confidence level with 42 degrees of freedom is: 1.682.
Therefore, we replacing:

The 90% confidence interval is (25.46, 28.34)