Answer :
We have a system of linear equations.
The most simple way to solve it is by substitution:
[tex]\begin{gathered} y=x+3 \\ 12x+y=-6 \\ \\ 12x+(x+3)=-6 \\ 12x+x+3=-6 \\ 13x+3=-6 \\ 13x=-6-3=-9 \\ x=\frac{-9}{13} \\ \\ y=x+3=\frac{-9}{13}+3=\frac{-9+3\cdot13}{13}=\frac{-9+39}{13}=\frac{30}{13} \end{gathered}[/tex]The values for the unknowns are x=-9/13 and y=30/13