1 hour and 15 minutes = 1.25 hours
1.25 hrs x speed rate = 80 miles
80 divided by 1.5 = rate per hour (64 mines)
OR
another concept is to think of the time as 5 15 minute segments.
80 divided by 5 = 16 miles every 15 minutes
16 times 4 (1/4 hours or 15 minutes)= distance in 1 hour (64 miles in 1 hour)