At a certain university, the average cost of books was $340 per student last semester and the population standard deviation was $90.

At a certain university, the average cost of books was $340 per student last semester and the population standard deviation was $90. This semester a sample of 45 students revealed an average cost of books of $370 per student. The dean of students believes that the osts are greater this semester with a 90% confidence. What is the critical value for this right tailed hypothesis and can the dean say that books are more expensive?