18. Find the sum of the coefficients of the polynomial
$$
\left(4 x^{2}-4 x+3\right)^{4}\left(4+3 x-3 x^{2}\right)^{2} \text {. }
$$
18. Ans: 1296
Let
$$
\left(4 x^{2}-4 x+3\right)^{4}\left(4+3 x-3 x^{2}\right)^{2}=A_{12} x^{12}+\cdots+A_{1} x+A_{0} \text {. }
$$

Substitute $x=1$ to obtain
$$
\begin{aligned}
A_{12}+A_{11}+\cdots+A_{1}+A_{0} & =(0-0+3)^{4}(4+0-0)^{2} \\
& =1296
\end{aligned}
$$