A restaurant manager claims that food servers at this restaurant make at least $15 per hour in tips. A random sample of 50 hours shows the mean amount of tips to be $12 per hour with standard deviation $0.75 per hour. What is the value of the test statistic that can be used to determine if there is convincing evidence that the mean amount of tips made per hour is less than the manager claimed? a. t = 9.172 b. t = -0.566 c. t = -0.08 d. t = -7.165