Question 255642
Very interesting problem. Easy solution.
{{{(x^10*y^(-8))^(-3)}}}
The important thing to remember is negative exponent means the reciprocal.
{{{3^(-3)}}} = {{{1/(3^3)}}}


{{{1/3^(-3)}}} = {{{1/(1/(3^3))}}}={{{3^3}}}

We have reciprocals of reciprocals in your problem.

{{{(x^2)^5}}}={{{x^10}}}


so 
{{{(x^10*y^(-8))^(-3)}}}=
{{{1/(x^10*y^(-8))^3}}}=

{{{1/(x^10/y^(8))^3}}}=
Let's deal with the reciprocal now

{{{(y^(8)/x^10)^3}}}=

{{{(y^(24)/x^30)}}}