Atrain travels 73 kilometers in 3 hours, and then 60 kilometers in 3 hours. what is the average speed

The answer is 22.17 km/hr. The total distance would be the sum of the first 73 kilometers and the second distance 60 kilometers, and the time the train took to cover that distance would be the sum of the first 3 hours and the second 3 hours. Since the average speed of the train is the total distance it traveled divided by the elapsed time to cover that distance, we have
     average speed = total distance/elapsed time
                              = (73km + 60km) / (3hr + 3hr)
                              = 133km / 6hr
                              = 22.17 km/hr

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.