Answer
a. See the graph.
b. The bar graph is generally easier to read and more flexible. This is because in pie chart, when two slices are about the same size, it is always unclear which value is larger. This distinction is clearer when comparing heights of bars in a bar graph. On the other hand, the bar graph can easily summarize how results compare for different groups ( to increase spending, decrease spending, same or others).
c. the bar graph is a better visual display when there are many categories.
