Tree Fiddy,
See how that first thing I listed has a number 1 behind it, and then see how that second thing has a number 2 behind it? Well, when you get down to the 6th thing, one of the Harleys, it has the number 6 behind it. We call that "sequential". It kind of like a trend, if you follow it to the end you can figure out how many things there are in total. Work on it, you'll get it.