How do u find federal income tax

You need to be more specific in your question. However, you can try this link to the IRS web site - here you can find the answer to any question you may have regarding US federal taxes:

Internal Revenue Service

You're going to need to provide a little bit more information. Is it for the employee or employer? Social security taxes or FICA is 7.65 % on an employees wages up to $84,900 and 1.45% on the amount above $84,900. It is paid by both the employee and employer. Unemployment tax is only paid by the employer and it's a little more complicated. The tax rate is 6.2 % to the federal government, but if the state imposes an unemployment tax then you can subtract that amount from 6.2; however, you can't decrease the tax rate to below 0.8%. This is the main part of income tax that basic accounting is concerned with.

I have form4868 whit amount $1300 where I have to put thios amount on form 1040