How much weight can you lose if you eat 8400 calories in a week?

It is impossible to tell since there are so many variables. It depends on how active you are, what you eat to get 8400 calories, how much sleep you get, etc. You may not even lose weight at all, even though it is highly unlikely. However, 8400 calories in a day is unhealthy, let alone a week. I don't think anyone is so fat that they need to resort to near-starvation to be healthy. You might even die if you go at that diet for more than a few weeks. I would recommend against it. In fact, if you are trying to lose weight, I suggest exercising for 30 to 60 minutes a day, using portion control, cutting out soft drinks and candy, and watching what you eat overall. Simply cutting calories will not get the results I am sure you are looking for.