Use the basic rules of exponents:
(a/b)^(-x)=(b/a)^x=b^x/a^x
[tex](\frac{2a^{-6}}{5b^4})^{-3}[/tex]
[tex]=(\frac{2}{5a^6b^4})^{-3}[/tex]
[tex]=(\frac{5a^6b^4}{2})^{3}[/tex]
[tex]=(\frac{5^3a^{6*3}b^{4*3}}{2^3})[/tex]
[tex]=(\frac{125a^{18}b^{12}}{8})[/tex]
