If you eat 1200 calories n burn 2800 calories a week how much weight would you lose?

It depends on what your base calorie need is.

A ballpark value is that you lose one pound for each 3500 cals lost.

So let's assume that your base need is 1800 cals/day. Means you're losing 600 cals/day or 4200 cals/week through diet alone. Then there's the 2800/week lost through exercise. 4200+2800= 7000 cals

Means there's a good chance you'll lose 2 pounds/week.

But maybe your base need is only 1500 cals, now you're only losing 2100 cals through diet and 5900 total. Then you won't be losing 2 lbs/week.