Actually Welcome to the concept of Parallel lines.
We must first understand that, Parallel Lines always have a same Slope, hence the 'm' value in y=mx+c equation will same, here it is '1/2' in the above equation,
There was only one car that went over the speed limit and it's car A (183). the other cars were all under and how i found this out was take 60 mph x hours n that's the miles they should of drove n that many hours if they are above it the miles will be higher.