Consider the function $f(x)$ below, Over what open interval$($s$)$ is the function increasing and concave down? Give your answer in intervat notation.

$f(x)=\frac{x^4}{4}-\frac{16x^3}{3}\frac{77x^2}{2}-98x9$

Enter $\frac{O}{?}$ if the interval does not exist.