Describe the Transformations Required to Obtain the Graph of the Function

Describe the transformations required to obtain the graph of the function f(x) from the graph of the function g(x) .
- $$f ( x ) = 3 \cos x ; g ( x ) = \cos x$$

A) Horizontal stretch by a factor of 3
B) Vertical stretch by a factor of 3
C) Vertical shrink by a factor of $\frac { 1 } { 3 }$
D) Horizontal shrink by a factor of $\frac { 1 } { 3 }$