We have
[tex]x+y=-9[/tex]x+9=y
We susbtitute
[tex]\begin{gathered} x+x+9=-9 \\ 2x=-9-9 \\ 2x=-18 \\ x=-9 \end{gathered}[/tex]then we find the value of y
[tex]\begin{gathered} y=-9+9 \\ y=0 \end{gathered}[/tex]In this case, the smaller number is -9
