First of all, notice that the given pattern is 1, 3, 6, 10, 15...
The pattern of this sequence is variable, the first difference is 2, then it's 3, then 5, then 5. So, the pattern increases one unit each time to get a new item.
Having said that, let's continue the pattern to find the eighth step.
[tex]15,21,28[/tex]
As you can see, the eighth term is 28.
Therefore, step 8 has 28 circles.
