Correct sentence: A tiger's roar is so loud that it travels a long way.
Why? When we say how loud something is and show the result, we usually use the pattern "so ... that ...". Adding the word that makes the sentence clearer for readers.
Notes for a 7-year-old:
- The original sentence sounds okay when you speak, but adding that makes it better for writing.
- Example: The drum was so loud that everyone covered their ears.
So use: A tiger's roar is so loud that it travels a long way.