firstly, change ur grades into letter grades
i.e. 90---A- (just an example, it's supposed to adjust to your school's standards
then, put letter grade into numerical values:
A=4.0
A-=3.7
B+=3.3
B=3.0
C+=2.3
C=2.0
C-=1.7
D=1.0
F=0.0
Finally, computing ur GPA
i.e.
eng101 4credits A 4*4.0=16
SOC102 3CREDITS A- 3*3.7=11.1
7CREDITS quality
attempted points=27.1
27.1 quality points/ 7credits=3.87GPA
Good luck! =) | 
