Given the system of equations:
[tex]\begin{gathered} x+y=6\text{ (eq. 1)} \\ y=-3x\text{ (eq. 2)} \end{gathered}[/tex]
Substituting equation 2 into equation 1 and solving for x:
[tex]\begin{gathered} x+(-3x)=6 \\ -2x=6 \\ \frac{-2x}{-2}=\frac{6}{-2} \\ x=-3 \end{gathered}[/tex]
Substituting x = -3 into equation 2:
[tex]\begin{gathered} y=-3(-3) \\ y=9 \end{gathered}[/tex]
The solution is (-3, 9)
