Question 622710
{{{f(x)=sqrt(x)}}} exists only for non-negative values of the variable {{{x>=0}}}
{{{g(x)=4x+12}}} (I think that is what you meant) is negative when {{{x<-3}}}.
In those cases, you can calculate {{{g(x)}}} but {{{f(g(x))=f(4x-12)}}} does not exist.
For all other values of x (when {{{x>=-3}}}) {{{f(g(x))}}} exists.
The domain for {{{f(g(x))}}} is all the x such that {{{x>=-3}}} so the answer is
{{{highlight(B)}}}.