In order to solve this system by substitution, we just need to apply the value of x from the first equation in the second one. So we have:
[tex]\begin{gathered} \begin{cases}x=9y-6 \\ 2x-8y=18\end{cases} \\ 2\cdot(9y-6)-8y=18 \\ 18y-12-8y=18 \\ 10y=30 \\ y=3 \\ \\ x=9y-6 \\ x=9\cdot3-6 \\ x=27-6 \\ x=21 \end{gathered}[/tex]So the solution to the system is (21, 3), that is, x = 3 and y = 21.
