This Fluency Activity is a part of the Lesson 10, Unit 4, Grade 3.<br> 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.