3 Answers

If your friend has the drive, and intelligence, it can happen...

There are a lot of variables.  The GPA is an accumulation of points from the classes you take.  In high school, I think all the classes have the same number of "units", which isn't the case in college. 
To establish a 3.5 overall GPA, if your friend has completed his sophomore year and is going to take the same total number of classes his junior and senior years as he has taken his first two years, he is going to need to average a GPA of 4.6. 
I think your friend should get his rear in gear and get the best grades he possibly can for the next two years and go to a community college for two years.  Not only will he save a boatload of money, but he can be active in community and school opportunities (which he should be doing the next two years of high school), and possibly be impressive enough to get into the school he wants for his final 2-3 years of college education. 
Here's a breakdown of what I'm talking about re: GPA
6 classes freshman year:  2.4 GPA
6 classes sophomore year:  2.4 GPA
6 classes junior year: 4.6 GPA
6 classes senior year:  4.6 GPA

Add 2.4, 2.4, 4.6, 4.6 = 14.0; now divide by 4 to get the overall average  3.5

No, it's not too late. He's got the rest of his H.S. years to bring it up. Tell him to talk to his teacher in whatever subject he's having trouble with ......so the teacher can tell him how to study or to do a project to bring up his grade.And he can get a tutor. Sometimes, if you just ask a student in your class to tutor you, they will. And he can learn the subject matter that way.