class Rect {
  constructor(w, h) {
    this.w = w;
    this.h = h;
  }
  area() {
    return this.w * this.h;
  }
}
console.log(new Rect(3, 4).area());

class Order {
  constructor(id) { this.id = id; }
}
class Delivery extends Order {
  constructor(id, address) {
    super(id);
    this.address = address;
  }
}
console.log(new Delivery(7, "Казань"));

class Bill {
  constructor(items) { this.items = items; }
  get total() { return this.items.reduce((s, p) => s + p, 0); }
}
console.log(new Bill([220, 150]).total);