When I run this code I get the error: "FrogStats.cs(14,20): error CS0103: The name `Convert' does not exist in the ....

namespace Treehouse.CodeChallenges
{
    class FrogStats
    {
        public static double GetAverageTongueLength(Frog[] frogs)
        {
            double total = 0;
            double AverageTongueLength = 0;
            double resultado = 0;


            for(int index = 0; index < frogs.Length; index++)
            {
                resultado = Convert.ToDouble(frogs[index]);
                total = total + resultado;

            }


            return AverageTongueLength = total / frogs.Length;
        }
    }
}

namespace Treehouse.CodeChallenges
{
    public class Frog
    {
        public int TongueLength { get; }

        public Frog(int tongueLength)
        {
            TongueLength = tongueLength;
        }
    }
}