ANSWER
B.[tex] (x + 6)^{4} [/tex]
EXPLANATION
The given functions are:
f(x)=x+6
and
[tex]g(x)= {x}^{4} [/tex]
We want to find
[tex]g(f(x)) = g(x + 6)[/tex]
This is the composition of functions, where one function becomes the input of the second function.
We plug in x+6 into the expression for g(x) to obtain,
[tex]g(f(x)) = (x + 6)^{4} [/tex]
The correct answer is B.