Final answer:
The radical expressions 7√7 and √63 cannot be combined.
Step-by-step explanation:
The radical expressions 7√7 and √63 cannot be combined to become one radical expression through addition or subtraction.
To combine radical expressions, the radicands (numbers inside the radical symbol) must be the same. In this case, 7√7 and √63 have different radicands (7 and 63), so they cannot be combined.