Help writing an explanation for a 3-day suspension

What happened was:
I drove my cousin to school one day where in the car he asked if he could store marijuana in the car so he wouldn’t have to carry it around during school. Stupidly and Immaturely I said yes and he ended up getting caught trying to sell the drug in my car. The school decided some of it was my fault so I was put on a 3-day suspension.

My question is what is the best possible way to explain this to a college I am applying to. (ie Univ of Pitt, Penn State, Univ of Delaware, Drexel).

Thanks

I think just tell them what you told us. Your cousin is your family member and you said yes to helping him out. In hindsight, you now understand that it was not a good decision to make and you should have declined and made him deal with his illegal behavior on his own. Tell the admissions committee that if faced with a similar situation in the future, you would not make that choice again, and that you would encourage your cousin to stop doing/selling drugs.

Thank you this helped a lot.