Class TestBox and Box to calculate area

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

namespace MyFirstConsoleApp.day2.examples
{
    class TestBox
    {
        static void Main()
        {
            Box ups, fedEx;
            ups = new Box();
            fedEx = new Box();

            ups.length = 10;
            ups.width = 5;
            double total = ups.CalculateArea(3, 4);

            fedEx.length = 7;
            fedEx.width = 5;
            total += fedEx.CalculateArea(5, 6);

            Console.WriteLine("total area = " + total);
            Console.ReadLine();
        }
    }
}
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MyFirstConsoleApp.day2.examples
{
    class Box
    {
        public int length;
        public int width;

        public double CalculateArea(int length, int width)
        {
            double area = length * width;
            // double area = this.length * this.width;
        Console.WriteLine("Area = " + area);
        return area;
        }
    }
}