Question 977398
(-3x^(-2)y^(0))^(-3)
Use parentheses to separate the exponents. 
This way it's clear and you don't need to explain.

{{{(-3x^(-2)y^(0))^(-3)=1/(-3x^(-2)y^(0))^(3)}}}
{{{(-3x^(-2)y^(0))^(-3)=1/(-3^(3)x^(-2*3)y^(0*3))}}}
{{{(-3x^(-2)y^(0))^(-3)=1/(-27x^(-6)y^(0))}}}
{{{(-3x^(-2)y^(0))^(-3)=-(x^6/27)}}}