有條數唔識做......help

做呢d數一定要有ed步驟
3x-y=0 (1)
x+y-8=0 (2)
sub.(1) into (2)
x+y-8=3x-y
y+y-8=3x-x
2y-8=2x
2y-2x=8
2(y-x)=8
y-x=2/8
y-x=4
y=4+x
sub.y=4+x into (1)
3x-4+x=0
4x-4=0
4x=4
x=4
sub.x=4 into y=4+x
y=4+4
y=8
the solution is x=4 y=8
3x-y = 0
x -1 13
只要計小中大三個數就行
3x-y = 0
x -1 1 3
y -3 3 9

X+y-8 = 0
x 0 3 6
y 8 5 2