a.
In the graph attached, blue bars represent the total distance of each trip and orange bars represent one third of the total distance for each trip.
d.
To get orange distances you have to divide the total distance by 3 for each trip, as following
1st trip: 300 km/3 = 100 km
2nd trip: 180 km/3 = 60 km
3rd trip: 200 km/3 = 66.67 km