To solve this question, let us determine the correct substitution step for solving the system of equations:

The system of equations is:

1. $y = x - 4$
2. $-2x + y = 18$

Substitution Method:

The idea is to substitute one equation into the other. Since equation 1 is already solved for $y$ ($y = x - 4$), the logical step would be to substitute this expression for $y$ into equation 2.

Substituting $y = x - 4$ into equation 2:

$-2x + (x - 4) = 18$

Simplify:

$-2x + x - 4 = 18$

This gives a simplified equation for $x$.

Correct Answer:

The first step should be:

• A. Substitute equation 1 into equation 2 for $y$, resulting in $-2x + (x - 4) = 18$.

If you'd like further explanation, please let me know! Here are 5 related questions and one tip:

Related Questions:

1. How do you solve the system of equations after the substitution step?
2. What other methods can be used to solve systems of linear equations?
3. Why is substitution effective for solving certain systems of equations?
4. How can you verify your solution to a system of equations?
5. What are some common mistakes to avoid when using the substitution method?

Tip:

Always simplify the equations fully after substitution to avoid errors when solving for variables.