How to get from charles de gaulle to Rue De La Convention in Paris?

I'm going to Paris this Saturday for 3 days and i'm not sure how to get the RER/Metro from Charles De Gaulle airport to my hotel which is on Rue De La Convention(Conventions on Line 12 is the nearest station) and how much would it cost? i've seen various ticket prices but not sure which one we would need and which lines to take to get there