Fazendo $f \circ g$: \begin{matrix} f[g(x)] + 2\cdot f[2 - g(x)] = (g(x)-1)^3 \\ \\ g(x) = 1-x \\ \\ f[g(x)] + 2\cdot f(1+x) = (-x)^3 \ \ \color{#3368b8}{(1)} \end{matrix} $\color{orangered}{Obs:}$ $f[g(x)] = f(1-x)$ Seja $h(x) = 1+x$, façamos $f \circ h$: \begin{matrix} f[h(x)] + 2\cdot f[2 - h(x)] = (h(x)-1)^3 \\ \\ f(1+x) + 2\cdot f(1-x) = (x)^3 \\ \\ f(1+x) + 2\cdot f[g(x)] = (x)^3 \ \ \color{#3368b8}{(2)} \end{matrix}Resolvendo o sistema composto por $(1)$ e $(2)$: \begin{matrix} f[g(x)] = x^3 \\ \\ Letra \ (C) \end{matrix}