用代入法解方程组(1)x=3,2x-y=8.(2)x=y-1,3x+2y=7.(3)x+2y=8,3x-y=3.
(4)2x+3y=12,x+4y=11.(5)3x+5y=21,2x-5y=-11.(6)6x-5y=3,6x+y=-15
(7)4s+3t=5,2s-t=-5.(8)3(x-1)=y+5,5(y-1)=3(x+5)