A large movie theater chain wanted to increase the average amount a customer spends on concessions per visit. They are considering implementing a new subscription service, with the hopes that it will make people visit more often, and that they will spend the money they save on ticket purchases on concessions instead. In order to implement this subscription service, the average amount a customer would need to spend on concessions per visit would have to be at least $15. They tested this service by randomly sampling 50 people. The mean of this sample was $17, and the sample standard deviation was 4.0. Determine the test statistic.