3x+y=7
9x-4y=-7
---
y=7-3x
9x-4(7-3x)=-7
9x-28+12x=-7
21x=28-7
21x=21
x=1
y=7-3.1
y=7-3
y=4
/x,y/=/1,4/
3x+y=7
9x-4y=-7
---
y=7-3x
9x-4y=-7
---
y=7-3x
9x-4(7-3x)=-7
y=7-3x
9x-28+12x=-7
y=7-3x
21x=28-7
---
y=7-3x
21x=21
---
y=7-3x
x=1
---
y=7-3.1
x=1
y=7-3
x=1
y=4
x=1
/x,y/=/1,4/