Answer
6
Work Step by Step
We know that if $A$ is a real number and $B\gt0$, then the graphs of $y=Asin(Bx)$ and $y=Acos(Bx)$ will have an period of $\frac{2\pi}{B}$.
Therefore, the period of the graph of $y=cos\frac{\pi}{3}x$ is $\frac{2\pi}{\frac{\pi}{3}}=2\pi\times\frac{3}{\pi}=\frac{6\pi}{\pi}=\frac{6\pi\div\pi}{\pi\div\pi}=6$.