Question 1163873
Let d = the total distance traveled
During the last 1/4 of the journey, the average speed was (7/8)*80 = 70 km/h
It took 2.5 h to travel d/4.  Thus (d/4)/70 = 2.5 -> d = 700 km
The total time is given by the distance traveled divided by the avg. speed:
t = 700/80 = 8.75 hours