Answer
Constant of Variation: $8$;
When $x=-0.5$, $y=-4$.
Work Step by Step
The model used for a direct variation is $y=kx.$ Given that $
y=4
\text{ when }
x=0.5
,$ the value of the constant of variation, $k,$ is
\begin{align*}
y&=kx
\\
4&=k(0.5)
\\\\
\dfrac{4}{0.5}&=k
\\\\
k&=8
\end{align*}
Hence, the direct variation equation is $
y=8x
.$ Substituting the given value, $x=-0.5,$ then the value of $y$ is
\begin{align*}
y&=8x
\\
y&=8(-0.5)
\\
y&=-4
\end{align*}
Hence, $
y=-4
$ when $x=-0.5$.
