Helen,
I am not sure what the average is, but Exam III in my view is one of the most difficult of the four. My own score was 84, and I am not sure how that is possible if all questions carry an equal weight (=1/36), as 84 is not a multiple of 1/36. I don’t know how the scoring works.
Other scores I remember are 75 and 72 that other people have reported to me, and one even had a 58 which is really disappointing as it was very close.
Keep us posted when you get your score! Good luck!
Mukul