Question

How to graph x+y=3 and x-y=1

Answer 1

Put them in y= mx+b format. . 
x+y=3 ---> y= -x+3 
x-y=1 ---> y= x-1 
The x's are your slope and the numbers are your y-intercept.
Hope it helps!

Answer 2

Isolate y in both the equations so
x+y=3                                                     x-y=1
y=-x+3                                                    y=x-1
your y-intercept is 3                                y-intercept is -1
and slope is -1/1                                      slope is 1/1