5x-12y=23,
x=(23+12y)/5
3(23+12y)/5+8y=10
69+36y+40y=50
76y=-19
y=-1/4.
x=(23-3)/5=4.
x=4,y=-1/4.
k=（1-2y）/3x
k=(1-(2*-1/4))/3*4
k=1/12