4x+2/5-5x-7/10=1
4x-5x=1-2/5+7/10
-x=13/10
x=-1.3
将x=-1.3代入6x+1=a(3x+2)-1
-1.3*6+1=a(-1.3+2)-1
a=(1-1.3*6+1)/(-1.3+2)
a=-58/7