The product of 2 and a number increased by 7 is -36

"The product" means you're multiplying the two numbers.
"a number" refers to a variable.
"increased" means you're adding.

2x + 7 = -36

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.