Sum types & match

An enum whose variants carry payloads is a sum type — a value is exactly one variant at a time. You handle each variant with an exhaustive match:

match s {
    Circle(r)  => return 3 * r * r
    Rect(w, h) => return w * h
}

The starter defines a Shape with Circle and Rect, and main asks for the area of a Rect(4, 5). Both arms currently return 0.

Your task: fill in the match arms so area returns the correct value for each shape. For the rectangle, that’s w * h. When correct, main returns 20.