input: 
  def extract_words(text: str, letter: str) -> List[str]:
      """Extract all the words starting with a specific letter from a given text.
      >>> extract_words('This is a sample sentence to test the program', 's')
      ['sample', 'sentence', 'test', 'the']
      >>> extract_words('Python programming is fun', 'p')
      ['Python', 'programming', 'programming']
      """
      words_list = [w for w in text.split() if w.startswith(letter)]
      return words_list
  
output:     words_list = [w for w in text.split() if w.lower().startswith(letter.lower())]
      return words_list