4 hours
Take 320 miles and divide by 65 mph. That gives you approx 4.92 hours at a constant velocity.
Matts speed was 320/5 miles per hour. At 320/5 mph he could have driven 9*320/5 miles = 9*64 = 576 miles.
320 miles, which would take about 5 and a half hours, according to Google Maps.
4.57 hours
4 hours 16 minutes @75 mph
320/60 = 51/3 hours = 5hours 20minutes
4 hours 55 minutes.
4 hours
4 hours 16 minutes.
6 hours, 24 minutes
5 hours 49 minutes.