What is the quickest I can lose 60 lbs?

I have been exercising and (for the most part) have been doing well on my diet. So far, I've lost 10 lbs and it's been a couple of months. If I am more consistent with my diet (pretty much just eating three 400 calorie meals a day) and exercise (kickboxing 1 hour 3 days a week and walking/jogging about 5 miles for 3-4 days) how quickly can I lose the weight? I know everyone is different, but generally, how many lbs a month can I lose?