What is the soulotion x+y=3, y=-x-1

The answer to x+y=3 is x=2 y=1. To y=-x-1 is x=2 y=-1

So iff you subitute y=-x-1 into the other equation (x+y=3)

you get x + (-x-1) = 3 then you get x-x-1=3 which is a false statment

if you change it so that y=-x-1=x+y=-1

y=-x-1

add x to both sides

x+y=-1

but the first equation said that x+y=3 so therefore the values of x and y in the two are not the same because x+y cannot equal 3 and - 1 at the same time