For a thesis project, a statistics student investigated whether athletes had better balance than non-athletes. The statistics student had 39 student athletes and 35 students who did not play any sport walk along a board that was 20 feet long by 2 inches wide that was raised 6 inches off the ground. The student recorded the number of times each participant touched the ground to maintain balance. The athletes had a sample mean of 4.7 touches with a sample standard deviation of 1.3 . The non-athletes had a sample mean of 5.1 touches with a sample standard deviation of 4.5 . Assuming the population variances are unequal, a hypothesis test for the difference between the two population means would have how many degrees of freedom