656
First, add the digits other than the units, 80 + 560 = 640. Remember that for a moment. Now, add the one's digits, 8 + 8 = 16. Now, add the 16 to the 640 to get 656. ---- Alternately, subtract 12 from 568 and give it to 88, so we have 100 + 556 = 656.