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 costs are greater this semester. What is the test value for this hypothesis?
a) 0.33
b) 0.67
c) 2.24
d) 15.00