input: Write a python function to find the most common words in a given text and return them sorted by their frequency in descending order.
  assert mostCommonWords("apple orange banana apple grape banana banana") == [('banana', 3), ('apple', 2), ('orange', 1), ('grape', 1)]
  assert mostCommonWords("dog cat dog bird cat dog") == [('dog', 3), ('cat', 2), ('bird', 1)]
  assert mostCommonWords("hello world hello") == [('hello', 2), ('world', 1)]
output: def mostCommonWords(text):
      from collections import Counter
      words = text.split()
      word_counts = Counter(words)
      return sorted(word_counts.items(), key=lambda item: item[1], reverse=True)