Question 70
Determine all pairs of functions $f, g$, $f : \mathbb{R} \to \mathbb{R}$, $g : \mathbb{R} \to \mathbb{R}$, that satisfy the equality
$$
g(f(x + y)) = f(x) + (2x + y)g(y)
$$
for all real $x, y$.
$$
g(f(x + y)) = f(x) + (2x + y)g(y)
$$
for all real $x, y$.