This data doesn't have anything to do with your case.
You need to prove that the black students being let in have substantially lower GPAs than the other students. Finding average high school GPA by race doesn't prove anything because you don't know if those are the same people going to the colleges.
You have to actually PROVE things, not find unrelated stats and make assumptions, I know that's hard, but that's why making claims without proof is frowned upon.