This Instructional Activity is a part of the Lesson 10, Unit 1, Grade 6. This activity allows students to practice identifying the base and height of triangles and using them to find areas. Because there are no directions on which base or height to use, and because not all sides would enable them to calculate area easily, students need to think structurally and choose strategically. All triangles in the problems have either a vertical or a horizontal side. Choosing such a side as the base makes it easier to identify the corresponding height. In some cases, students may opt to use a combination of area-reasoning strategies rather than finding the base and height of the shaded triangles and applying the formula.