Chapter 2 - Systems of Linear Equations and Inequalities - 2.3 Solving Systems of Equations Using the Elimination Method - 2.3 Exercises - Page 161: 36

Substitution

We want to use the substitution method here. In one equation, one variable is expressed in terms of another, so we can easily use this expression to substitute for the variable in the other equation; this equation will then only have one variable which we can solve for.