Every body is different. A pound is 3500 calories. The more muscle you have, the faster you'll burn the fat.
You need weight training 3 times a week, alternating days. Cardio is fine too.
You have to eat and burn calories to take you under your maintenance calories. For instance, there are calculators out there to do this...my maintenance is 1800 calories a day. If I were to eat 1500 calories a day, that's 300 calories a day less than what it takes to maintain my body weight. 300 times 7 days is 2100 calories. Not quite a pound. So, let's say my goal is to workout 3 times a week and add cardio 2 times and I burned 1900 calories through that. 1900 plus 2100 is 4000 calories.
One pound being 3500 calories, I've just lost just over a pound in a week.
4 1/2 pounds a month times 6 is 27 pounds.
Plus, people that are very overweight, tend to lose more in the beginning because there's water weight etc. that comes off faster.
But that's the basic foundation.
I'm doing a program just for women at
http://inshapenow.net. It's amazing with great support from women doing this program or have already succeeded.
Just remember...
Less calories, build muscle through weights, eat protein and carbs through veggies and fruit. You need fat in your diet, don't cut it all out. There are good fats. Dump the diet sodas, they won't help, and actually have been proven to hurt weight loss.
Good luck