input: Write a python function to find the most used words in a given string and return them with their counts.
  assert most_used_words("apple apple banana banana orange orange orange") == [('orange', 3), ('apple', 2), ('banana', 2)]
  assert most_used_words("cat bat mat rat cat mat") == [('cat', 2), ('mat', 2), ('bat', 1), ('rat', 1)]
  assert most_used_words("one two two three three three") == [('three', 3), ('two', 2), ('one', 1)]
output: def most_used_words(s):
      from collections import Counter
      
      words = s.split()
      word_counts = Counter(words)
      sorted_word_counts = sorted(word_counts.items(), key=lambda x: (-x[1], x[0]))
      
      return sorted_word_counts