Independence is a condition of a nation, country, or state in which its residents and population, or some portion thereof, exercise self-government, and usually sovereignty, over the territory. The opposite of independence is the status of a dependent territory.
Depending on the state. If it's a four year federal sentence you will have to do 85% ,or they takeoff 54 days a year for good behavior. Most states abdopted the NERA Act for federal funding (No Early Release Act). Meaning if you're incarcerated for a violent crime you will be required to do 85% of your sentence.
How long you work is up to you. If you are a making good grades and are good at studying, try working for 30 to 45 minutes, then take a 5 or 10 minute break to have a snack or do something physical. Doing exercise also helps wake your brain back up!