Okay send your work and I will help you
95% C.I. = mean + or - 1.96(standard deviation / sqrt(sample size))
95% C.I. = 57 + or - 1.96(3.5/sqrt(40) = 57 + or - 1.085 = 57 - 1.085 to 57 + 1.085 = 55.92 to 58.09
Therefore, 95% of the mean will occur in the interval 55.92 to 58.09
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