Question about Computability

Question

Q:Suppose $U(n,x)$ is Gödel Universal Function, show that there is $n$ such that $U(n,x)=n+x$ for all $x$ I did some proof but I am mot sure if I am right. Let's consider a computable binary function $V(n,x)=n+x$ By theorem, there has to exist a number $n$ such that $U(n,x)=V(n,x)$. Therefore, there exist n such that $U(n,x)=n+x$. I am not quite sure this proof is right or not. If it is not correct, could anyone give me some hit for it? Thank you.