ok let me explain i started at 81 in july 2005 before I had my daughter, lost 4 kg after having her, then went from 77kg to 52 in just under 8 months.
How have I done it? Well, I have done a lot of exercise (1 hour a day minimum) for example power walking, cycling, jogging, Pilates &Yoga. I now attend a gym that a lady in my city set up herself that has circuit classes (stationary bike, rower, cross trainer, mini trampoline, steps, jumping rope, punching bag), classes for ab exercises,bums,legs and thighs, and one just for abs.
Nutrition wise... well I tried a lot of diets and all were successful for me (but not every diet is for every person) and only changed diets because I got bored. But I suggest just eating lots of vegetables, lean meats (chicken,fish,lean beef), not having too much sugar. a treat once a week or every two weeks also won't destroy all your hard work either.