I want to add a value to my list but it says "system.array does not contain the definition of add"

Question

using System;
using System.Collections;

namespace Ejercicio_5
{
    class Program
    {
        public static void Main(string[] args)
        {
             
            var numero = new [] {2,5,7,4,1,5,7222};
            int Num=0;
            numero.add(90);
         
             foreach (var d in numero)
             {
                if ( Num < d )
                {
                    Num = d;
                }
             }
                    
             Console.WriteLine(Num);
             Console.ReadKey();
        }
    }
}