3x-y=2k-1 (1)
4x+2y=k(2)
(1)×2+(2)
10x=5k-2x=(5k-2)/10
(2)×3-(1)×4
10y=-5k+4 y=(-5k+4)/10
x-y=(5k-2+5k-4)/10=(10k-6)/10=k-3/5
x-y