This Instructional Activity is a part of the Lesson 16, Unit 6, Grade 7. Students describe rectangular regions that result from slicing a right rectangular prism by a plane perpendicular to one of the faces. Students examine the cross sections of solid figures in the next four lessons. In Lessons 16 and 17, students examine slices made parallel or perpendicular to a face of a solid before moving to angled slices in Lesson 18.