Based on these factors: A=4 pts, B=3 pts, C=2 pts, D=1 pt, F=0 pts, you would add up the point values of all of your grades. Also assuming that your letter grades are on a ten point scale, (i.e. An "A" is between 90-100%), you would get 8 points in "A" grades, 9 points in "B" grades, and 2 points in "C" grades and here are GPA Calculator High School 4.0 Scale.
We would need to know what is the maximum amount of points you can earn.
If 40 points is 100%, Divide 38.5 by 40. You get a 85%, which is an B.