Abstract class and Interface

//First Base Class
class Monitor : ITV
{
    // Fields
    public int Number_HDMI_Port { get; set; }
    public int Number_USB3_Port { get; set; }
    // Constructors
    // other Methods
    public void Power(bool on)
    {
        if (on) Console.WriteLine(" the TV is ON");
        else Console.WriteLine(" the TV is OFF");
    }
    // Indexers
}
// Second Base Class
class HomeTheater : ITV
{
    // Fields
    public int Number_HDMI_Port { get; set; }
    public int Number_USB3_Port { get; set; }
    // Constructors
    // other Methods
    public void Power(bool on)
    {
        if (on)
        {
            Console.WriteLine(" Shows the Menu for ON the Screen");
            Console.WriteLine(" The TV  is ON");
        }
        else
            Console.WriteLine(" the TV is OFF");
    }
    // Indexers
}
// Interface
interface ITV
{
    // Properties
    int Number_HDMI_Port { get; set; }
    int Number_USB3_Port { get; set; }
    // Methods
    void Power(bool on);
}

// Base Class
abstract class TwoDShape
{
    // Fields
    private double width;
    public double Width
    {
        set { this.width = value < 0 ? -value : value; }
        get { return this.width; }
    }
    private double height;
    public double Height
    {
        set { this.height = value < 0 ? -value : value; }
        get { return this.height; }
    }
    // Constructors
    // other Methods
    public abstract double Area(); // abstract Method so You Must own Class change to Abstract Class
    // Indexres
}
class Triangle : TwoDShape
{
    // Methods
    public override double Area() // Override Area Method
    {
        return (Width * Height) / 2;
    }
}
class Rectangle : TwoDShape
{
    // methods
    public override double Area() // own implimentation
    {
        return Width * Height;
    }
}