& gt=90 5.0
& lt90 & gt=85 4.5
& lt85 >； =80 4.0
& lt80 >； =75 3.5
& lt75 >=70 3.0
& lt70 >=65 2.5
& lt65 >=60 2.0
Convert it into corresponding grade points first, and then average it according to credits.
Ps: My GPA for the first three years was 4.87.