Answer
$$ G'(2)= -18.$$
Work Step by Step
Given $ F(x)=f(g(2x))$, then we have $ G'(x)=2f'(g(2x))g'(2x)$ and hence
$$ G'(2)=2f'(g(4))g'(4)=2f'(2) (3)=6(-3)=-18.$$
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