Answer
$8 \sin(\dfrac{\pi}{2}) t $
Work Step by Step
Amplitude, $ A=|8|=8$
Now, $ f=\dfrac{\omega}{2 \pi} \implies \omega =2 \pi f $
and period, $ P=\dfrac{2 \pi}{\omega} $
So, $\omega =2 \pi (\dfrac{1}{4})=\dfrac{\pi}{2}$
Therefore, $ d=A \sin \omega t=8 \sin(\dfrac{\pi}{2}) t $
