These don't correspond to A, B, and so on. 
It was just easiest to separate them by 10's.

 

Grade

# of students

91-100

 0

81-90

16

71-80

 28

61-70

 22

51-60

 13
41-50 12
31-40 6
21-30 2
0-20 0

mean

65

median

69