Your instructor took a random sample of 18 students to examine the number of hours per week students surf the Internet for either personal information or material for course activities. The sample mean response was 6.65 hours and the sample standard deviation was 0.85 hours. Based on these results, and assuming normality for the population distribution of surfing time in hours, the instructor constructed a confidence interval extending from 6.05 to 7.08 hours per week for the population mean. What is the confidence level used for this interval?