Taxes on pension?

i have a pension of 50000 dollars per year.i get a check for 3500 monthly.my problem is i cannot figure out how to withhold app175 dollars per monthly check fed taxes.it says i must enter a number 0 ,1 ,2 etc.then theres a box if iwant more taken out.how do i utilyze these two procedures to get to 175 fed withholding on my 3500 monthly check