The 12 measurements below depict the times for a manual screwdriver to remove a particular side clip.

33.8 31.6 28.5 29.9 29.8 26.0 35.7 27.2 29.1 32.1 26.1 24.1

Supposing these measurements are of a normal distribution N(μ,s^2), find the point estimates for μ and s. Consequently, find a 95% one-sided confidence interval that
provides an upper bound for μ.
Answer..--> [29.49, 3.41, (0, 31.259)]

i've got the answer correct for μ and s..
However.. the positive interval,

i've got 29.49 + (2.201) x {(3.41) / (sqrt(12))} = 31.657

The answer should be 31.259..
is the answer is wrong or my calculation is wrong?