If $3$ dice are thrown together the no. of ways in which the sum of numbers appearing on the dice is $n$, is? $ \ $ $9 \leq n \leq14$
My try: $(x^1+x^2+x^3+x^4+x^5+x^6)^3$
The sum of the coefficients of $x^9$ to $x^{14}$ should be found. But I am getting stuck up in calculations. Now I have started doubting this method.