Lesson objective: Write and solve equations in one variable to solve systems of equations by substituting equivalent terms for the other variable.

This lesson helps to build procedural skill with solving systems of equations. Equations are used here because they show how equivalent quantities can be represented in different ways. This work develops students' understanding that systems of equations can be solved by writing equations in one variable.

Students engage in Mathematical Practice 1 (make sense of problems and persevere in solving them) as they make sense of expressions and variables in an equation and use equivalent expressions to write equations in one variable from two equations in two variables.

**Key vocabulary:**

- substitution property of equality
- transitive property of equality