What does "what scale would be appropriate to graph the data? " mean?

I think it means which graph is the best at representing the data or data set.

For example if you were to graph the population of an animal you would use a line graph to represent the data

If you were determining how much percentage you would get  a job you would use a pie graph. Etc

so, converting firstly the mixed fractions to improper fractions and then "adding".