This Instructional Activity is a part of the Lesson 23, Unit 7, Grade 8. There are three phases of the modeling in this lesson: assigning variables, determining the equation, and analyzing results. Many questions are included to guide students' thinking, but the activity may be structured in many different ways, including students working collaboratively in small groups to make sense of and persevere in solving the problem. Students may benefit from a demonstration of this situation. Consider using a notecard leaning against a box to show what flush means and how the ladder would slide down the wall.