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Given $$f ( x ) = \sqrt { x }$$ and $$g ( x ) = 3 x + 12$$ , find the domain of $$f ( g ( x ) )$$ Use interval notation and type 'inf for $$\infty$$
$$f(x)= \sqrt x\ (x\ge0)\\g(x)= 3x+ 12\ge0\Rightarrow x\ge- 4\\x\in[- 4,+ \infty)$$