A4. The solution to the equation $2 \cdot 3^{x-3}+3^{x-2}+3^{x-1}=14 \cdot 3^{5}$ is
(A) $x=2$
(B) $x=8$
(C) $x=-8$
(D) $x=-2$
(E) $x=0$
A4. Let's write $14 \cdot 3^{5}=3^{x-3}\left(2+3+3^{2}\right)=14 \cdot 3^{x-3}$. It follows that $3^{5}=3^{x-3}$ or $x=8$.