In this lesson, students use hanger diagrams as a way to represent equivalence. Students may have seen this representation in prior grades, but now they explore how to deal with shapes of unknown weight. Students continue to describe moves that maintain equivalence for the representations and should recognize that, as long as the unknown weights are equivalent, they can be removed equally from each side of the diagram. As they move fluently between hanger diagrams and algebraic equations representations, students must reason abstractly and quantitatively (MP2).