\(9^{12}.27^5.81^4=\left(3^2\right)^{12}.\left(3^3\right)^5.\left(3^4\right)^4\)
\(=3^{24}.3^{15}.3^{16}\)
\(=3^{55}\)
\(64^3.4^5.16^2=\left(4^3\right)^3.4^5.\left(4^2\right)^2=4^{18}\)
\(25^{20}.125^4=\left(5^2\right)^{20}.\left(5^3\right)^4=5^{52}\)
\(x^7.x^4.x^3=x^{14}\)
\(3^6.4^6=\left(3.4\right)^6=12^6\)
\(8^4.2^3.16^2=\left(2^3\right)^4.2^3.\left(2^4\right)^2=2^{23}\)
\(2^3.2^2.\left(2^3\right)^3=2^{14}\)