This culminating lesson is optional. In this lesson students work on several tasks that combine circumference and area ideas and computations. First, students are given a design for a stained-glass window and the prices of the different components. They decide if it would be possible to produce the window for a certain amount of money. Students must make some assumptions about the shapes in the design and about how the different materials are sold.

The following two activities are optional, so teachers can choose what best fits the needs of their students. The first optional activity asks how scaling the window will affect the cost, bringing in ideas from a previous unit. Since measurements of both length and area are involved, the total cost does not simply increase by the scale factor nor by the square of the scale factor. In the second optional activity, students invent their own design for a stained-glass window that could be produced given a cost constraint. The series of tasks provides many opportunities to engage in different aspects of mathematical modeling (MP4).