Suppose that a certain company claimed that the average life span of their AA tire is 44,975miles. But you, as a consumer had doubts about the life span of the new tire and thought that maybe it is less than what the company claimed. So you collected the lifespan of 92 AA tires. You found out that the average life span of the sampled AA tires was only 40,523 miles with standard deviation of 7,218 miles. The null hypothesis in this study is H_o: = 44,975 and the alternative hypothesis is H_a:u < 44,975. What is the test statistics? Write the answer with 2 decimal places.