input: Write a function to find the first letter of an array of words and return the longest word.
  assert find_first_letter_longest_word(['Hello', 'Hi', 'House', 'Hat']) == 'House'
  assert find_first_letter_longest_word(['Apple', 'Apricot', 'Avocado']) == 'Avocado'
  assert find_first_letter_longest_word(['Banana', 'Blueberry', 'Blackberry', 'Bit']) == 'Blackberry'
output: def find_first_letter_longest_word(words):
      first_letter = words[0][0]
      longest_word = ''
      for word in words:
          if word.startswith(first_letter) and len(word) > len(longest_word):
              longest_word = word
      return longest_word