Answer
\begin{equation}
\begin{aligned}
y&= 5(4^{-1/6})^{t}\\
&=a4^{kt} \\
a&= 5\\
k&= {-1/6}\\
\end{aligned}
\end{equation}
Work Step by Step
Given
$$y = 5(0.5)^{t/3} $$
Rearrange the function to get:
\begin{equation}
\begin{aligned}
y&= 5(0.5)^{t/3}\\
&= 5(0.5^{1/3})^{t}\\
&= 5(1/2^{1/3})^{t}\\
&= 5(1/2^{2/6})^{t}\\
&= 5(1/4^{1/6})^{t}\\
&= 5(4^{-1/6})^{t}\\
y&=a4^{kt} \\
a&= 5\\
k&= {-1/6}\\
\end{aligned}
\end{equation}