input: 
  def replace_string(sentence: str, old_word: str, new_word: str) -> str:
      """ Replace a given word in a sentence with another word.
      >>> replace_string("I love walking on the beach", "walking", "swimming")
      'The new sentence is: 'I love swimming on the beach''
      >>> replace_string("Python is fun", "fun", "awesome")
      'The new sentence is: 'Python is awesome''
      """
  
output:     new_sentence = sentence.replace(old_word, new_word)
      return f"The new sentence is: '{new_sentence}'"