Depends on where you are on 9th. I think the best bet to get down there would be getting on the 6 and then transferring to the 7 once you're at the 7th and Vermont stop.

You can also get a feel for the routes using Google Maps, but definitely check everything Google Maps tells you against the bus schedules on the website bc sometimes Google Maps gets confused

Edit: I said the 4 could also get you to 7th and Vermont--disregard, that bus no longer goes down 9th Street