$\large{\left(x^3 + 3x^2 + 3x + 2 \right) P(x-1) =\left(x^3 - 3x^2 + 3x - 2 \right)P(x)}$

Let $P(x)$ be a polynomial with real coefficients such that it satisfies the above equation $\forall \ x \in \mathbb R$, where $P(2)=84$. Submit the value of $P(10)$ as your answer.

**Bonus** - Generalize $P(x)$.