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You haven't mentioned your height. Anyways you seem fit. If you want to lose the belly, you must avoid the sedentary lifestyle. Make sure to do jogging or brisk walking for atleast 40 minutes a day. Sit ups will help tone your belly. Drink plenty of water. Eat plenty of fresh fruits and green leafy vegetables. Avoid eating junk food, chips, colas, etc. Eat more wheat, ragi, soya bean. Stop smoking
and drinking alcohol. If you do these things, you may get into shape and expect great results within 2-3 months.