y$($x$)=($x$-4)/($x$^2),$ what is y$\text{'}($x$)$ and y$\text{'}\text{'}($x$)$ Find the interval$($s$)$ on which f is concave up$.($Enter your answer using interval notation.$)$

Find the interval$($s$)$ on which f is concave down. $($Enter your answer using interval notation.$)$