Trying to add GrossWeight each time it shows up in the list

     private int CalculateGrossWeightOfCars() {

            int totalGrossWeight;
            
            foreach (int GrossWeight in RailCars) {
                GrossWeight += GrossWeight;
            }
        } 

     private int CalculateGrossWeightOfCars() {

            int totalGrossWeight;
            
            foreach (int GrossWeight in RailCars) {
                GrossWeight += GrossWeight;
            }
        } 

 public class Engine
    {
        public readonly string Model;
        public readonly string SerialNumber;
        public readonly int Weight;
        public readonly int HorsePower;

        public Engine(string model, string serialNumber, int weight, int horsePower) {

 public class Engine
    {
        public readonly string Model;
        public readonly string SerialNumber;
        public readonly int Weight;
        public readonly int HorsePower;

        public Engine(string model, string serialNumber, int weight, int horsePower) {

 public Train(Engine engine) {
            Engine = engine;
            RailCars = new List<RollingStock>();
        }   

 public Train(Engine engine) {
            Engine = engine;
            RailCars = new List<RollingStock>();
        }