Jsing the definition $of$ derivative $of$ a function $at$ a point, $f^{\text{'}}(a)=\underset{h0}{lim}\frac{f(a+h)-f(a)}{h},$ find the slope $of$ the curve $at$ the given points $or$ state that the slope $is$ undefined.

$f(x)=\frac{-6}{-7x+4}$

$Ata=1,$the slope $is$

$Ata=\frac{4}{7},$ the slope $is$