Константин Кавенский

Полагаю, что вам нужно что-то вроде этого: jsfiddle

так сойдет?

using System;

namespace auto
{
    class Program
    {
        public class Auto
        {
            private int _speed = 0;
            private int _time = 0;
            private string name_car = string.Empty;

            public int Speed { get { return _speed; } set { _speed = value; } }
            public int Time { get { return _time; } set { _time = value; } }
            public string Name_car { get { return name_car; } set { name_car = value; } }

            public void Drive()
            {
                Console.WriteLine(Speed * Time + " class Auto" + " name car: " + Name_car);
            }
        }


        public class fastCar : Auto
        { 
            public void fastDrive(int time, string name)
            {
                Console.WriteLine(Speed * time * 2 + " class fastCar" + " name car: " + name);

            }

        }

        public class slowCar : Auto
        { 
            public void slowDrive(int time, string name)
            {
                Console.WriteLine(Speed * time / 2 + " class slowCar" + " name car: " + name); 
            }

        }
        static void Main(string[] args)
        {
            fastCar x = new fastCar(); 
            x.Speed = 100;
            x.Time = 15;
            x.Name_car = "fastCar-x";
            x.Drive();
            x.fastDrive(x.Time, x.Name_car);


            slowCar y = new slowCar();
            y.Speed = 100;
            y.Time = 15;
            y.Name_car = "slowCar-y";
            y.Drive();
            y.slowDrive(y.Time, y.Name_car);
            Console.ReadLine();
        }
    }
}

п.с. логику лучше переделать под норму "don't repeat your self"

хотя бы вот так:

using System;

namespace auto
{
    class Program
    {
        public class Auto
        {
            private int _speed = 0;
            private int _time = 0;
            private string name_car = string.Empty;

            public int Speed { get { return _speed; } set { _speed = value; } }
            public int Time { get { return _time; } set { _time = value; } }
            public string Name_car { get { return name_car; } set { name_car = value; } }

            public void Drive()
            {
                Console.WriteLine(Speed * Time + " class Auto" + " name car: " + Name_car);
            }
        }


        public class fastCar : Auto
        { 
            public void fastDrive()
            {
                Console.WriteLine(Speed * Time * 2 + " class fastCar" + " name car: " + Name_car);

            }

        }

        public class slowCar : Auto
        { 
            public void slowDrive()
            {
                Console.WriteLine(Speed * Time / 2 + " class slowCar" + " name car: " + Name_car); 
            }

        }
        static void Main(string[] args)
        {
            fastCar x = new fastCar(); 
            x.Speed = 100;
            x.Time = 15;
            x.Name_car = "fastCar-x";
            x.Drive();
            x.fastDrive();


            slowCar y = new slowCar();
            y.Speed = 100;
            y.Time = 15;
            y.Name_car = "slowCar-y";
            y.Drive();
            y.slowDrive();
            Console.ReadLine();
        }
    }
}