Question: in an effort to reduce energy costs a major university...

In an effort to reduce energy costs, a major university has installed more efficient lights as well as automatic sensors turn the lights off when no movement is present in a room. Historically, the cost of lighting an average classroom for 1 week has been $249. To determine whether the changes have significantly reduced costs, the university takes a sample of 83 classrooms. They find that the average cost for 1 week is $249 with a standard deviation of $65. When testing the hypothesis (at the 5% level of significance) that the average energy use has decreased from the past, what is the test statistic?