Subtract the area of this square from the rectangle. Break the shape into two squares and a rectangle. Calculate the area of each shape. \(4 \times 4 = 16~\text{cm}^2\), \(4 \times 4 = 16~\text{cm}^ ...

For example, you can define an interface for a shape that has functions to calculate its area and perimeter, and then create structs for different shapes that implement those functions.