Line 12 is for a state two letter code (IA=iowa) if state taxes are withheld...leave 12 blank and make 14 blank too IF there is a 0.00 in 14.
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.......now, if box 10 has a $$ amount, you need to select "More than one state" (if you are in the interview)...or "XX" if you are int the Review/Error check section.
Then study the situation to decide if you want to mess with it anymore. "More than one state" is always acceptable, bus sometimes a bit of state taxes can be saved by indicating exactly how much of box 10 came from bonds issued by only your state.