McGill grading scale:

A 85+
A- 80-84
B+ 75-79
B 70-74
B- 65-69
C+ 60-64
C 55-59
D 50-54
F 49-

Applied to the first exam, which consisted of four questions worth 25 points each, this scale yields roughly the following per-question grading scale:

A 21.5+
A- 20-21.5
B+ 19-20
B 17.5-19
B- 16-17.5
C+
15-16
C 14-15
D 12.5-14
F 12.5-

 

Applied to the second exam, which consisted of three questions worth about 33 points each, this scale yields roughly the following per-question grading scale:

A 28+
A- 26.5-28
B+ 25-26.5
B 23-25
B- 21.5-23
C+
20-21.5
C 18-20
D 16.5-18
F 16.5-