stuff.cs

    class Program
    {
        public class TimeTargetCategory
        {
            public Guid Id { get; set; }
            public Guid TimeTargetId { get; set; }
            public Guid CategoryId { get; set; }
            public decimal? MondayTarget { get; set; }
            public decimal? TuesdayTarget { get; set; }
            public decimal? WednesdayTarget { get; set; }
            public decimal? ThursdayTarget { get; set; }
            public decimal? FridayTarget { get; set; }
            public decimal? SaturdayTarget { get; set; }
            public decimal? SundayTarget { get; set; }
        }

        static void Main(string[] args)
        {
            var timeTargetCategory = new TimeTargetCategory
            {
                MondayTarget = 6,
                TuesdayTarget = 6,
                WednesdayTarget = 6,
                ThursdayTarget = 6,
                FridayTarget = 6,
                SaturdayTarget = 6,
                SundayTarget = 6
            };

            var result = timeTargetCategory.MondayTarget ?? 0 +
                         timeTargetCategory.TuesdayTarget ?? 0 +
                         timeTargetCategory.WednesdayTarget ?? 0 +
                         timeTargetCategory.ThursdayTarget ?? 0 +
                         timeTargetCategory.FridayTarget ?? 0 +
                         timeTargetCategory.SaturdayTarget ?? 0 +
                         timeTargetCategory.SundayTarget ?? 0;

            Console.WriteLine("Result: {0}", result);
        }
    }