How long would it take an 18 year old guy who is 200 pounds to get a six pack?

hi, i just lost 78 pounds im now 200, but now all the skin is hanging down because i was fat and now its just flabby skin, i was wondering how long would it take for me to tone those ab mussels and get a six pack? and what would i have to do to get it? thank you very much :D