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