Combining like terms
[tex]\begin{gathered} 6x+4y-6x+9y=46+6 \\ 6x-6x+4y+9y=46+6 \\ (6-6)x+(4+9)y=52 \\ 0\cdot x+13y=52 \\ 13y=52 \\ y=\frac{52}{13}=4 \end{gathered}[/tex]Think of y = 4 as y=f(x)=4
This means that for any value of x you replace, you will always get y = 4