10^m=2
10^(n-1)=1/5
10^n/10=1/5
10^n=10/5=2
10^(-4m+3n)
=10^(-4m)*10^3n
=(10^m)^(-4)*(10^n)^3
=2^(-4)*2^3
=2^(-4+3)
=1/2