Train A leaves Valley station at 2:00 pm traveling south at a rate of 50 miles per hour. Train B leaves Valley station at 6:15 pm the same day and travels north. At 8:00 pm the same day, Train A and Train B are 405 miles apart. What is the average rate of Train B?
(A) 52 mph
(C) 60 mph
(B)55 mph
(D) 75 mph