using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<List<int>> valuesCollection = new()

        {

            new() { 2, 4, 4, 2, 5 },

            new() { 1, 3, 6, 3, 8 },

            new() { 0, 3, 9, 0, 0 },

        };

        CalculateSumsInArray(valuesCollection);

        CalculateSumsInList(valuesCollection);

    }

    private static void CalculateSumsInArray(List<List<int>> valuesCollection)

    {

        var indexCount = valuesCollection[0].Count;

        var sums = new int[indexCount];

        Array.Fill(sums, 0);

        foreach (var values in valuesCollection)

        {

            for (var i = 0; i < sums.Length; i++)

            {

                sums[i] += values[i];

            }

        }

        Console.WriteLine("Sums (array): " + string.Join(", ", sums));

    }

    private static void CalculateSumsInList(List<List<int>> valuesCollection)

    {

        var sums = valuesCollection[0].ToList();

        foreach (var values in valuesCollection.Skip(1))

        {

            for (var i = 0; i < sums.Count; i++)

            {

                sums[i] += values[i];

            }

        }

        Console.WriteLine("Sums  (list): " + string.Join(", ", sums));

    }

}

​