Basically, how many would a person be able to have to still have a 3.9, not a 3.8. What is the maximum, considering that they have all A’s in everything else. Over four years worth of courses, not one, so around 30 credits.
Sorry, I honestly just don’t want to do the work to figure this out 
Depends on how many courses you take in those four years?
Let’s say 30
(# A’s x 4.0 + # A-'s x 3.7) / (# A’s + # A-'s)
This assumes all classes are worth the same number of credits.
Change 3.7 to whatever A-'s are worth at your school if it’s different (3.67, etc.).
Thank you!
Some schools like the UC’s ignore the + and -