I can't seem to figure out the second half of this question:

I know that μ = μ of sample = 91.625, but i need to find the rangeConsider the sample 100 91 91 86 90 91 90 94 from a normal population with population mean μ and population variance σ^{2}. Find the 95% confidence interval for μ.

I also know the standard deviation of the sample of the population is σ/sqrt(n)

the answer s 91.63±3.37 but I'm not sure where 3.37 comes from, since the σ the sample population is 4.03/sqrt(8) = 1.425