This Problem Set is a part of the Lesson 10, Unit 4, Grade 3. In this lesson, students apply knowledge of the distributive property to find area. They relate earlier experiences decomposing arrays to using the distributive property to determine the unknown side length of a rectangle. For example, if a rectangle has an area of 72 square units, students might decompose the area into an 8 by 5 rectangle and an 8 by 4 rectangle.