Question 252064
3x+ y=12 
y=-3x+12 (red line)
9x+3y=36
3y=-9x+36
y=-9x/3+36/3
y=-3x+12 (green line)
These 2 lines are identical thus they overlap.
{{{ graph( 300, 200, -6, 5, -10, 14, -3x +12, -3x +12) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 14, of TWO functions -3x +12 and -3x +12).