Quadratic Equation And Inequalities

Let $\mathbb{R}$ denote the set of all real numbers. Let $a_i, b_i \in \mathbb{R}$ for $i \in \{1, 2, 3\}$.

Define the functions $f: \mathbb{R} \to \mathbb{R}$, $g: \mathbb{R} \to \mathbb{R}$, and $h: \mathbb{R} \to \mathbb{R}$ by

$f(x) = a_1 + 10x + a_2 x^2 + a_3 x^3 + x^4$

$g(x) = b_1 + 3x + b_2 x^2 + b_3 x^3 + x^4$

$h(x) = f(x + 1) - g(x + 2)$

If $f(x) \neq g(x)$ for every $x \in \mathbb{R}$, then the coefficient of $x^3$ in $h(x)$ is