4 miles per day is quite the distance to walk and you'll certainly lose some weight if you can walk 4 miles per day everyday.
If you walk at 3 mph for 80 minutes then that would mean you would walk a total of 4 miles and walking 4 miles per day you would burn more than 950 calories per day.
So yes you can certainly lose quite a bit of weight walking 4 miles per day plus you'll be helping to improve your overall health.