Here are a few rules with exponents that apply here:
Firstly, solve the outer exponent:
[tex](\frac{4mn}{m^{-2}n^{6}})^{-2}=\frac{4^{-2}m^{-2}n^{-2}}{m^{-2*-2}n^{6*-2}}=\frac{4^{-2}m^{-2}n^{-2}}{m^4n^{-12}}[/tex]
Next, divide:
[tex]\frac{4^{-2}m^{-2}n^{-2}}{m^4n^{-12}}=4^{-2}m^{-2-4}n^{-2-(-12)}=4^{-2}m^{-6}n^{10}[/tex]
Next, convert the negative exponents:
[tex]4^{-2}m^{-6}n^{10}=\frac{n^{10}}{4^2m^6}=\frac{n^{10}}{16m^6}[/tex]
Your final answer is n^10/16m^6 , or B.