RoomCarpet

public class RoomCarpet {

    private RoomDimension size;
    private double carpetCost;

    public RoomCarpet(RoomDimension dim, double cost)
    {
        this.size = dim;
        this.carpetCost = cost;
    }

    public double getTotalCost()
    {
        return size.getArea() * carpetCost;
    }
}