We have,
$y=\frac{c}{t}$
$ \Rightarrow \frac{d y}{d t}=\frac{-c}{t^{2}}$
Also, $ x=c t$
$\Rightarrow \frac{d x}{d t}=c$
$\therefore \frac{d y}{d x}=\frac{(d y / d t)}{(d x / d t)}=\frac{\frac{-c}{t^{2}}}{c}=\frac{-1}{t^{2}}$
On putting $t=2$, we get
$\frac{d y}{d x}=-\frac{1}{4}$