It depends where exactly you are because it's not accessible to some parts of Baltimore, but the MARC train leaves from Camden Yards and will get you to college park in about 45 minutes. From there you can take the green line 2 or 3 stops to ft Totten, transfer to the red line and you'll be in silver spring after a few stops. Probably take you about an hour and fifteen minutes when all is said and done.

Bethesda would probably take longer as you would have to take the Penn Station marc to union Station and then hop on the red line and go all the way through DC.

Honestly, I would just be ecstatic if there was reliable transit that could get me downtown, which there isn't unless you live right along the light rail line or the subway line. The busses here are so chaotic.