Answer
$\{(-1,2)\}$
Work Step by Step
Graph each line
(plot two points per line, such as the interceptcs)
$ \begin{array}{lllllll}
& & & & & & \\
x+y=1 & & & | & y-x=3 & & \\
x=0 & & y=0 & | & x=0 & & y=0\\
& & & & & & \\
0+y=1 & & x+0=1 & | & y-0=3 & & 0-x=3\\
y=12 & & x=1 & | & y=3 & & x=-3\\
(0,1), & & (1,0) & | & (0,3) & & (-3,0)
\end{array} $
Plot the pairs of points and the accompanying lines.
Determine intersection points, if any.
(see attached image)
There is an intersection point,
the solution set is $\{(-1,2)\}$
