input: from typing import Tuple
  
  def replace_string(sentence: str, old_word: str, new_word: str) -> Tuple[str, str]:
      """ Replaces a given word in a sentence with another word and returns the new sentence.
      >>> replace_string("I love walking on the beach", "walking", "swimming")
      ("I love walking on the beach", "I love swimming on the beach")
      >>> replace_string("Python is great", "great", "awesome")
      ("Python is great", "Python is awesome")
      """
      new_sentence = sentence.replace(old_word, new_word)
      return sentence, new_sentence
output:     new_sentence = sentence.replace(old_word, new_word)
      return sentence, new_sentence