Question 136885
sometimes it's easier to graph & then solve:
the solution here is (2,1)
X+Y=3
Y=-X+3 (RED LINE)
X-Y=1
-Y=-X+1
Y=X-1 (GREEN LINE)
 {{{ graph( 300, 200, -6, 5, -10, 10, -x +3, x-1) }}} 
(graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions -x +3 and x -1).