How do you address an envelope with a PO Box?

PO Box xxxx

(City), (State) (Zip Code)-xxxx

If there are more than four numbers in the P.O. Box number append the last four numbers of the P.O. Box after the zip code. If there are less than four numbers in the P.O. Box then precede that number with the requisite number of zeroes so that four digits follow the zip code.