Question 76198
x+y=4                                                                           x=-1
.
Substitute x=-1 for x in the first equation and solve
x+y=4
(-1)+y=4
-1+y=4
-1+1+y=4+1
y=5
.
Check by plugging-in the values for x and y and solve:
x+y=4
(-1)+5=4
4=4 [checks out]