(a) Find $\displaystyle \frac{dy}{dx}$ as a function of $t$ for the given parametric equations. $$\begin{array}{r@{\,}c@{\,}l} x & = & t - t^{3} \cr y & = & -6 - 8 t \end{array}$$ $\displaystyle \frac{dy}{dx} =$ .

(b) Find $\displaystyle \frac{dy}{dx}$ as a function of $t$ for the given parametric equations. $$\begin{array}{r@{\,}c@{\,}l} x & = & 9 t + 6 \cr y & = & t^{3}-t^{8} \end{array}$$ $\displaystyle \frac{dy}{dx} =$ .