Question

multiple-choice question
once you have the value of one variable, what do you do with it?
solve an equation for the other variable so you can find your second number.
substitute it into one of the equations in order to find the other variable.
put a box around your answer. you have found the solution.

Explanation:

In systems of equations (e.g., solving linear systems), once one variable's value is found, the standard method is substitution into an equation to find the other variable. The first option implies solving a new equation (not typical after finding a variable), and the third is about formatting, not solving. So the correct approach is substituting the known variable value.

Answer:

B. Substitute it into one of the equations in order to find the other variable.