A bird flies against a wind that is going 4 miles per hour and takes 2 hours to travel a certain distance. When flying with th current, the bird only takes 0.5 hours to travel the same distance. Approximately how fast would the bird fly, in miles per hour, without wind current, assuming it flies at a constant rate? (A) 6.0 mph (B) 6.5 mph (C) 6.67 mph (D) 7.0 mph (E) 7.5 mph