Error: An object reference is required to access non-static member `Treehouse.CodeChallenges.LexicalAnalysis.WordCount'

using System.Collections.Generic;

namespace Treehouse.CodeChallenges
{
    public class LexicalAnalysis
    {
        public Dictionary<string, int> WordCount = new Dictionary<string, int>();

        public void AddWord(string word)
        {
            int num;
            if (WordCount.TryGetValue(word, out num))
            {
                WordCount[word]++;
            }
            else
            {
                WordCount.Add(word, 1);
            }
        }

        public static Dictionary<string, int> WordsWithCountGreaterThan(int num)
        {
            Dictionary<string, int> newDic = new Dictionary<string, int>();
            foreach (KeyValuePair<string, int> pair in WordCount)
            {
                if (pair.Value>num)
                {
                    newDic.Add(pair.Key, pair.Value);
                }
            }
            return newDic;
        }
    }
}