How much state income tax supposed to take out on 18000?

I can give you an answer for New Hampshire: none (New Hampshire doesn't have a state income tax).

For any state that does have a state income tax, it's going to be a lot more complicated because it depends on a number of factors. Your best bet is to consult an accountant or tax attorney in your state and ask them what it should be for the specific case you have in mind.