Zappos is an online retailer based in Nevada and employs 1,300 employees. One of their competitors, Amazon.com, would like to test the hypothesis that the average age of a Zappos employee is less than 36 years old. A random sample of 22 Zappos employees was found to have an average age of 33.9 years. The standard deviation for this sample was 4.1 years. Amazon would like to set = 0.025. The test statistic for this hypothesis test would be ________.