Question $6.$ Find the derivative for each function. $(Youdo$ not have $to$ simplify$)$

$(a)f(x)=-\frac{x^2}{4}+5x^{-9}-\frac{1}{\sqrt[\phantom{2}]{x}}$

$(b)f(x)=\frac{1}{4}(x^4+8)$

$(c)y=\sqrt[\phantom{2}]{x}+x^3+x-1$