1.8, 2.85, 3.90, 4.95, 6
To find the rule for this sequence, you find the difference between 2 numbers ..
1.8 + n = 2.85
n = 1.05
2.85 + n = 3.90
n = 1.05
3.90 + n = 4.95
n = 1.05
4.95 + n = 6
n = 1.05
As you can see, each have a difference of +1.05
The rule for this sequence is adding 1.05