Final Histogram.
with suggested letter grade equivalents

00:
01:
02:
03:
04:
05:
06:
07:
08: X
09:
10: XX          C
11: XXX
12: XX
13: X
14:     --------------------
15: X
16:
17:
18: X
19:             B
20: XX
21:
22: X
23: X
24: X
25:         ---------------
26:
27: X
28: XX          A
29: X
30:
31: X
32:
33:
34:
35:
36:
37: X
38: X
39:
40: