Some textbooks and professors do it slighly different. I think this isn't much different, if any, from what you are being taught. To get the numbers to go on the bottom, you subtract .5 from each left bound, 35-.5 = 34.5, 41-.5 = 40.5, etc. To get the last one, since the difference between each is 6, add 6 to the last one, 71.5+6 = 77.5.The frequency polygon is just a bunch of lines connecting the middle of the tops of the histogram bars, so it's this green zig-zagging line: But usually you are required to mark off the midpoints of the class intervals under each bar, instead of the midpoints with the .5's. Like the horizontal axis is marked off below: And maybe you're not supposed to show the histogram but just the green zig-xag line, which is the frequency polygon. Edwin