How to exercise to lose weight?

If I go on the treadmill 3 days a week for a half hour, and attend the gym 2 days a week or a half hour-will I lose weight? I gained14 pounds in a course of 6 months and my stomach is now huge. Will crunches and sit ups work as well? I do plan on eating healthier as well. I'm afraid of gaining weight from muscle ON TOP of my fat. Please tell me what to do and not do. Thanks!
How to exercise to lose weight?
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