using System;

using System.Linq;

using System.Collections.Generic;

​

public class StudentScore

{

    public string StudentName { get; set; }

    public int Score { get; set; }

    // other properties

}

​

public class StudentScoreSum

{

    public string StudentName { get; set; }

    public int ScoreSum { get; set; }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        List<StudentScore> dbScores = new()

        {

            new() { StudentName = "Bob", Score = 5 },

            new() { StudentName = "Bob", Score = 5 },

            new() { StudentName = "Bob", Score = 5 },

            new() { StudentName = "John", Score = 4 },

            new() { StudentName = "John", Score = 4 },

            new() { StudentName = "Michael", Score = 3 },

            new() { StudentName = "Michael", Score = 3 },

            new() { StudentName = "Michael", Score = 4 }

        };

        List<StudentScoreSum> scoreSum = dbScores

            .GroupBy(s => s.StudentName)

            .Select(scoresByStudent => new StudentScoreSum {

                StudentName = scoresByStudent.Key,

                ScoreSum = scoresByStudent.Sum(s => s.Score)})

            .ToList();

        Console.WriteLine(string.Join(Environment.NewLine, scoreSum.Select(s => $"{s.StudentName}: {s.ScoreSum}")));

    }

}

​