The table above shows some values of $x$ and their corresponding values $f(x)$ for the linear function $f$. If $f(x)=mx+b$, what is the value of $m+x_0$, where $x_0$ is the $x$-coordinate of the $x$-intercept of the graph of $y=f(x)$ in the $xy$-plane?

x	3	4	5
f(x)	12	8	4