To go from function f to function g you dilated f fromthe x-axis in the y direction also known as a vertical stretch.
To find the factor of the vertical stretch you identify the change in y-values for the same x-value; approximate changes:
For x=4
In f y= 2, in g y=4
For x=8
In f y=3, in g y=6
As you can see above the y-values duplicate, then the factor is 2.
The vertical stretch can be written in the next form:
a is the factor of dialtion.
Then, to produce g, function f was vertically stretch by a factor of 2, function g is defined as g(x)=2log(x)