Tax rates are different in every state and there is not a formula that applies to everyone.
Taxes are different in each state, and even in each city, because of different tax rates. Also, each employee can decide how much they would like to withhold based on family size and other income. We also don't know if there are garnishments being taken out of their wages.
You can look up your tax rates based on where you live and your income bracket. There are a lot of internet sites that can help, including taxfoundation.org.