Question 199218
x+y=9 or y=-x+9 (red line)
x-y=-1 or -y=-x-1 or y=x+1 (green line)
{{{ graph( 300, 200, -6, 5, -10, 10, -x +9, x +1) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions -x +9 and x +1). 
Solution (4,5)