Twice a year, for all four years of college, you used your credit card to pay for books and supplies, which amounts to $516 a semester.
In addition to that, you charged a yearly spring break trip, which averages about $700 per trip, each of the four years.
Finally, each of the 48 months you spent as a college student, you ended up charging some eating out, entertainment, clothes, etc. After interest and making your minimum monthly payment, you end up adding a balance of $100 per month.