In order to estimate the average time spent on the computer terminals per student at a local university, data were collected from a sample of 81 business students over a one-week period. Assume the population standard deviation is 3.9 hours. If the sample mean is 8 hours, then the 95% confidence interval is approximately _____.

a. 6.36 to 9.65 hours

b. 6.04 to 9.96 hours

c. 4.10 to 11.90 hours

d. 7.15 to 8.85 hours