If the function is discontinuous at $x=0$ and$f(0)=4.5$ . And as $x$ approaches $0$, the value of function nears $3$.
Does the limit in this case exist?
Imho ,it does and equals $3$ but one of my friend disagreed.
I'd be grateful if someone even hints at my error.
Thank you.

The limit exists, and is $3$. The fact that the limit is not the value of the function there is what tells you the function isn't continuous.