To become an actuary, it is necessary to pass a series of 10 exams, including the most important one, an exam in probability and statistics. An insurance company wants to estimate the mean score on this exam for actuarial students who have enrolled in a special study program. They have no other information about scores, so they take a sample of 6 actuarial students in this program and determine that their scores are: 5, 8, 7, 6, 5, and 7. This sample will be used to calculate a 90% confidence interval for the mean score for actuarial students in the special study program. The critical value used in constructing a 90% confidence interval is