For which pair of functions is open paren f circ g close paren times x is equal to 12 x ?

To find (f ∘ g)(x), substitute g(x) into f(x). For choice C, g(x) = 3x and f(x) = 4x, so f(g(x)) = 4(3x) = 12x. This matches the expression in the question, so the correct pair is f(x) = 4x and g(x) = 3x.

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