To rounding numbers, there's a rule that most people now. 0, 1, 2, 3, 4 you leave the number the same. 5, 6, 7, 8, 9 you round the number up. So you'll round 4 to 5 so now you have 0.85. Now the 4 is now a 5 so you'll round 8 up to a 9. Now your answer is 0.9
I hope this helps!