8. The time required for assembly by skilled labor was measured on 100 units of the same type of transistorized assembly. The average time was 10.2 minutes with a standard deviation of 1.8 minutes. What is the margin of error of this confidence interval, for the actual average assembly time, having a 90% confidence level?

a) 0,231

b) 0,464

c) 0,353

d) 0,296

e) 0,259