原式=4*(-6)-(6x+4y)+15=-24+2*6+15=3
=12x+8y-6x+15-4y =6x+4y+15 =2(3x+2y+6)+3 =3
=12x+8y-6x+15-4y=6x+4y+15=2*3x+2*2y+2*6+3=2(3x+2y+6)+3=3