ArrayData.cs

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

 class Program
 {
    static void Main(string[] args)
    {
        int[] numbers = AddNumbers(12, 15);

        Console.WriteLine(numbers[0]);
        Console.WriteLine(numbers[1]);
        Console.WriteLine(numbers[2]);
    }

    private static int[] AddNumbers(int a, int b)
    {
        int[] data = new int[3];
        int result = a + b;

        data[0] = a;
        data[1] = b;
        data[2] = result;

        return data;
    }
}