Answer
$-8$
Work Step by Step
If $x=x(t), \quad y=y(t)$, then
$\displaystyle \frac{dy}{dx}=\frac{(\frac{dy}{dt})}{(\frac{dx}{dt})}$
$\displaystyle \frac{dy}{dt}=\frac{d}{dt}[4t-1]=4$
$\displaystyle \frac{dx}{dt}=\frac{d}{dt}[1-\frac{1}{2}t]=-\frac{1}{2}$
$\displaystyle \frac{dy}{dx}=\frac{4}{-\frac{1}{2}}=-8$
