How to find coeeficient of in a binomial expression

I have to find coefficient of $x^3$ in $(x + 1)^n + (x + 1)^{n – 1}(x + 2) + (x + 1)^{n – 2}(x + 2)^2 + ldots + (x + 2)^n$ and I cannot get a starting point as to how to solve this.