What's the answer to these questions

21) 6d^2 - 15d + 4

24) 2s^2 + s - 15

27) 14t^2 + 26t - 4

The major difference is that a histogram is only used to plot the frequency of score occurrences in a continuous data set that has been divided into classes, called bins.  bar charts, on the other hand, can be used for a great deal of other types ofvariables  including  ordinal  andnominal  data sets.