a: \(7^{12}\cdot27^4=7^{12}\cdot\left(3^3\right)^4=7^{12}\cdot3^{12}=\left(7\cdot3\right)^{12}=21^{12}\)
b: \(15^4:125^3\)
\(=\dfrac{5^4\cdot3^4}{\left(5^3\right)^3}=\dfrac{5^4\cdot3^4}{5^9}=\dfrac{3^4}{5^5}\)
c: \(\left(0,125\right)^8:64^4\)
\(=\left(0,125\right)^8:\left(8^2\right)^4\)
\(=\left(\dfrac{0.125}{8^2}\right)^4=\left(\dfrac{0.125}{64}\right)^4=\left(\dfrac{1}{512}\right)^4\)
d: \(4^9\cdot5^{27}=4^9\cdot\left(5^3\right)^9=4^9\cdot125^9=\left(4\cdot125\right)^9=500^9\)
e: \(3^{12}\cdot2^{16}=\left(3^3\right)^4\cdot\left(2^4\right)^4=27^4\cdot16^4=\left(27\cdot16\right)^4=432^4\)