C# CS0120 - non-static member reference error

I review the answer on another CS0120 error question, but I'm not following it. The variable name is exactly the same as the private variable I set as a double before the method. I originally thought this was because I was trying to reference the "Frog" property "TongueLength", but when I removed that code, it looks like its just the name of the variables I'm using. I'm getting the below error on all of the variables I'm calling.

error CS0120: An object reference is required to access non-static member `Treehouse.CodeChallenges.FrogStats._totalTongueLength'

Sorry, I thought it was downloaded with the question. Odd, pretty sure I checked that. In any event, see below:

FROG STATS CLASS

namespace Treehouse.CodeChallenges { class FrogStats { private int _tongueLength; private int _sumOfTongueLength; private double _avgTongueLength; private int _numberOfFrogs;

    public static double GetAverageTongueLength(Frog[] frogs)
    {

          for (int i = 0; i < frogs.Length; i++)
          {

             Frog frog = frogs[i];
             _tongueLength = frog.TongueLength;
             _sumOfTongueLength = _tongueLength + _sumOfTongueLength; 

          }
      _numberOfFrogs = frogs.Length += 1;
      _avgTongueLength = _sumOftongueLength /= _numberOfFrogs;


    }
}

}

FROG CLASS

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

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

}

For some reason it isn't formatting the first couple lines of code properly?!