Answer: First option.
Explanation:
The missing picture is attached.
You can use these methods to solve a System of Equations and find the value of the variables:
A. Substitution method.
B. Elimination method.
In this case, given the following System of equations:

The most efficient method to solve it is the Substitution Method. The procedure is:
Step 1: Solve for one of the variables from the most convenient equation.
Step 2: Make the substitution into the other equation and solve for the other variable in order to find its value.
Step 3: Substitute the value obtained into the equation from Step 1 and evaluate, in order to find the value of the other variable.
Based on this, you can identify that first step to solve the given System of equations, is solving for "x" from the second equation:
