129-69-31十7=(129+7)-(69+31)=136-100=36
129-69-31十7=130-1-70+1-30-1+7=130-100+6=30+6=36
129-69-31+7=129+7-(69+31)=136-100=36
129-69-31+71=129+71-(69+31)=200-100=100