Simplify the following expression to simplest form using only positive exponents.
(125x^-9 y^-21)4/3
(125x^-9 y^-21)4/3
= 125^(4/3) * x^(-9(4/3)) * y^(-21(4/3))
= 125^(4/3) * x^(-12) * y^(-28)
= (5^3)^(4/3) / (x^12) / (y^28)
= (5^4) / (x^12) / (y^28)
= 625 / x^12 / y^28