a)\(16^6:4^2=\left(4^2\right)^6:4^2=4^{12-2}=4^{10}\)
b)\(18^8:9^4=\left(2.9\right)^8:9^4=2^8.9^8:9^4=2^8.9^4=\left(2^2.9\right)^4=36^4\)
c)\(125^4:25^3=\left(5^3\right)^4:\left(5^2\right)^3=5^{12}:5^6=5^6\)
d)\(12^n:2^{2n}=\left(2^2.3\right)^n:2^{2n}=2^{2n}.3^n:2^{2n}=3^n\left(n\inℕ^∗\right)\)