8 miles. Imagine travelling at 1 mph, it would take you 8 hours. At 2 mph, it would take you half the time (4 hours), 3 mph = a third, 4 mph = a quarter, 5 mph = a fifth, and so on. Therefore, using this principle, 3 mph = 2 hours and forty minutes, added to 4 mph = 2 hours, giving you your 4 hours and 40 minutes.