10^m=20
10^n=0.2
10^m÷10^n=20÷0.2
10^(m-n)=100
m-n=2
2m-2n=4
9^m÷3^2n
=(3^2)^m÷3^2n
=3^2m÷3^2n
=3^(2m-2n)
=3^4
=81