if i earn 12,800 per year and i am paid 12 times per year and i claim 1 exemption and i am taxed by my state at 3% how much is withheld per pay period?

Are you talking about federal or state withholding? Most states (and IRS) have a progressive tax rate than increases with income about a certain threshhold income level, below which no tax is owed. At $12,800 annual income, I doubt whether you need to withhold any income tax at all. Your biggest withholding will be for Social Securiy (FICA) -- which could be as high as 8% of income.