Over a 2 mile course a car travels 15 mph over the first mil

Over a 2 mile course, a car travels 15 mph over the first mile.
What speed does the car need to travel over the 2nd mile to average 30 mph over the whole course

It\'s not possible.
15 mph for 1 mile takes 4 minutes
30 mph for 2 miles also takes 4 minutes, so time is up. He can\'t do it.