Without Graphing the Function, Determine Its Amplitude or Period as Requested

Multiple Choice

Without graphing the function, determine its amplitude or period as requested.
- $y = 4 \cos \frac { 1 } { 3 } x \quad$ Find the period.

A) 4
B) $\frac { 4 \pi } { 3 }$
C) $6 \pi$
D) $\frac { \pi } { 3 }$