A survey of Mr. Huang's math class showed the following times it took for his students to complete their homework (in minutes): 15, 20, 20, 25, 25, 25, 25, 30, 30, 30, 30, 35, 35, 35, 45, 45, 45, 50, 50, 50. If you want to interpret the average time spent on homework (mean) and the spread of the data (range), what type of graph should you use to display the data set?