This Instructional Activity is a part of the Lesson 2, Unit 1, Grade 6. In grade 3, students recognized that area is additive. They learned to find the area of a rectilinear figure by decomposing it into non-overlapping rectangles and adding their areas. Here students extend that understanding to non-rectangular shapes. They compose tangram pieces-consisting of triangles and a square-into shapes with certain areas. The square serves as a unit square.