Answer:
If they drive an average of 60 miles per hour the last day it will take them 2.5 hours.
4 hours at 60 miles per hour = 4*60 = 240 miles
6 hours at 65 miles per hour = 6*65 = 390 miles
This is a total of 630 miles. There are 780-630=150 miles left; if they average 60 miles per hour, that would be 150/60 = 2.5 hours.
Explanation: