From the text: Solving linear equations, an important mathematical technique at the core of the Algebra 1 curriculum, forms an essential foundation for more advanced work. Too often, developing fluency with linear equations entails plowing through pages of repetitive exercises. How can students master this topic while using their mathematical sense-making faculties? In addition to generating essential practice with the technique of solving linear equations, this lesson on expression polygons engages students in authentic mathematical thinking. The expression polygon task is a rich task that students of all ages from grade 6 upward can access.