1.3600*8/9=3200
2.设爸爸今年上半年平均月收入为X X*5/6=3600 X=3600*6/5=4320
3.设妈妈前年上半年平均月收入为X X+X*1/5=3600 X*6/5=3600 X=3600*5/6 X=3000