x-y=9m则x=y+9m,因x+2y=5m所以3y+9m=5m,则3y=-4m推出：y=-4m/3；
2（x-y）=2*9m,则（x+2y）+2(X-y)=5m+2*9m,则3x=23m推出：x=23m/3；
所以3x+2y=3*23m/3+2*（-4m/3）=23m-8m/3=61m/3=17
推出：m=17*3/61=51/61