Answer
amplitude: $3$
period: $\frac{2\pi}{3}$
Work Step by Step
If a function has form $y=A\cos(\omega x)$, then there $|A|$ stands for the amplitude.
First we identify $\omega$ and $A$ from the form of $y=A\cos{(\omega x)}$.
Hence, $A=|-3|=3$, $\omega=3.$
To get the period $T$ we can use the formula: $T=\frac{2\pi}{\omega}$ to obtain
$T=\frac{2\pi}{3}$