This Problem Set is a part of the Lesson 20, Unit 3, Grade 7. In this lesson, students use prior knowledge to use the sum and/or difference of the areas to find unknown composite areas. Students find the area of regions in the coordinate plane with polygonal boundaries by decomposing the plane into triangles and quadrilaterals, including regions with polygonal holes. Students find composite areas of regions in the coordinate plane by decomposing the plane into familiar figures (triangles, quadrilaterals, circles, semicircles, and quarter circles).