Question 243536
3u+v=6
3x+y=6
y=-3x+6 (red line)
3u=v+12
3x=y+12
y=3x-12 (green line)
{{{ graph( 300, 200, -6, 5, -15, 10, -3x +6, 3x -12) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 15, of TWO functions -3x +6 and 3x -12). 
These 2 equations are independent (exactly 1 solution).