The 6th grade semester grades for a single class were as follows:

97, 95, 90, 67, 89, 90,

87, 85, 82, 76, 75, 74

62, 60, 56, 82, 94, 82

61, 83, 92, 81

What is the difference between the mean semester grade for the class and the highest semester grade in the class?