BaseAvalonia/AvaloniaApplicationBase/Models/Count.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaApplicationBase.Models
{
    public partial class Teacher
    {
        public string count
        {
            get
            {
                long? c = 0;
                foreach (var item in TeacherCourses)
                {
                    if (item.TeacherId == Id)
                    {
                        c += Convert.ToInt32(item.Course.Time);
                    }
                    else
                    { 
                    
                    }
                }
                if (c > 0)
                {
                    return "Курсы в объёме " + c + " часов.";
                }
                else
                {
                    return "Курсы не найдены.";
                }
            }
        }
    }
    
}