Answer
(a) $3$, $4\pi$, $\frac{1}{4\pi}$.
(b) see graphs.
Work Step by Step
(a) Given $y=3cos(\frac{1}{2}t)$, we can identify the amplitude as $3$, period as $\frac{2\pi}{1/2}=4\pi$, and frequency of the motion as $\frac{1}{4\pi}$.
(b) see graphs.