task2(a)

using System;
using System.Linq;

namespace task2
{
    public static class ArrayExtensios
    {
        public static int SumArray(this int[] a)
        {
            int res = 0;

            foreach (int item in a)
                res += item;

            return res;
        }
    }

    class Program
    {
        public static void Main (string[] args)
        {
            int[] array = new int[]{ 10, 20, 30, 90, 80, 70 };
            int res = array.SumArray();

            Console.WriteLine ("Sum of array's items = {0}", res);
        }
    }
}