3A+5B=3(A+B)+2B
2A-B+2B-A=A+B=X+Y.
2A-B+4B-2A=X+2Y3B=X+2Y
3A+5B=3(A+B)+2B=3(X+Y)+2/3(X+2Y)=化简就行了,这里的x,y是当作已知数来算的,不然算不出数来的