1.a=2b+3 a=3b+20 =>2b+3=3b+20 =>b=-17 a=-31
2.x=6y-7带入 x-y=13 =>6y-7-y=13 =>y=4 x=17
3.x-y=4 =>x=y+4带入 4x+2y=-1 =>4(y+4)+2y=-1 =>y=-6/17 x=6/7
4.5x-y=110=>y=5x-110 带入9y-x=110 =>9(5x-110)-x=110 =>x=25 y=15