Hi, 

c​=0.95, o=3.9 ​, n=100

df = 100-1 = 99 , c=0.98​ 

Using online Calculator/above values for t-value:   z= 1.98 (t-critical value)

ME =

ME = = .77

Assuming mean = 0

-.77 <  < .77

ONe may use charts or online calculators for t-values used for small samples

For Large Samples, following z-values are used

 = CI	z = value

90%	z =1.645

92%	z = 1.751

95%	z = 1.96

98%	z = 2.326

99%	z = 2.576 

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