(2) Solve the system using the substitution method.
\[
\begin{array}{l}
x+3 y=8 \\
y=3 x-4
\end{array}
\]

Step 1 ：Given the system of equations: \[\begin{array}{l} x+3 y=8 \\ y=3 x-4 \end{array}\]

Step 2 ：The substitution method involves solving one of the equations for one variable in terms of the other variable and then substituting this expression into the other equation. In this case, the second equation is already solved for y, so we can substitute the expression for y from the second equation into the first equation. This will give us an equation with only x's that we can solve.

Step 3 ：Substitute y from the second equation into the first equation: \[x + 3(3x - 4) = 8\]

Step 4 ：Simplify the equation to find the value of x: \[10x - 12 = 8\] which gives \[x = 2\]

Step 5 ：Substitute x = 2 back into the second equation to find the value of y: \[y = 3(2) - 4\] which gives \[y = 2\]

Step 6 ：Final Answer: The solution to the system of equations is \(\boxed{x = 2, y = 2}\)