Your total distance calculation was correct, nice work!
To obtain the average speed, you must divide the total distance by the total time.
Total distance = 86.45km, now we need to get time into hours by dividing the total minutes by 60.
Do not forget to add in the time spent eating and refueling (14.9 minutes), one answerer above forgot about this period of time..
Total time = 109.1 minutes, (109.1/60) = 1.818 hours
Tota distance = 86.45km/
Total time = 1.82 hours
Average speed= 47.50km/hr
I did some rounding that may not have been correct, but the calculations are correct.
i love physics!