85 of a 10 year sentence is 8 and 1/2 years or 8 years and 6 months.
So that means if someone gets a 10 year prison sentence and they have to serve at least 85 percent of that 10 year sentence then the person in prison would have to stay in prison for at least 8 years and 6 months before they could be considered for parole.
Some prisoners do only server half of their prison sentence or more than half of their prison sentence and sometimes get out early for good behavior.
For example if someone gets sentenced to 25 years to life in prison then they would have to serve at least 25 years of their life in prison.
Then the person could be considered for parole after 25 years.
However it does not mean the person will get released from prison after 25 years but in some cases they might.
If someone gets a life without parole sentence that means the person will never get out of prison alive and must remain in prison until they die.
For example in Oklahoma, someone serving time after a conviction becomes eligible for parole after completing 1/3 of their sentence.
So if they were sentenced to 10 years, they will only be eligible for parole after (roughly) 3 years and 4 months.
Some prisoners only serve half of their prison sentence because it's is intended to allow some rehabilitation in the community, while keeping release dates consistent and prison numbers down.
Those guilty of more serious crimes - such as serious sexual assaults or grievous bodily harm - will spend a greater part of their sentence in jail.