I believe there is a typo in the problem. It should be:1.8, 2.85, 3.90, 4.95, 6
If that was the case, the answer will be easy.
In this sequence, the rule is start at 1.80 then keep add 1.05. You can try to put them all into the equation
1.80 + 1.05= 2.85
2.85+ 1.05= 3.90
3.90+ 1.05= 4.95
4.95+ 1.05= 6.00
